85 results on '"Klaas Nauta"'
Search Results
2. PAH Growth in Flames and Space: Formation of the Phenalenyl Radical
- Author
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Zachariah D. Levey, Benjamin A. Laws, Srivathsan P. Sundar, Klaas Nauta, Scott H. Kable, Gabriel da Silva, John F. Stanton, and Timothy W. Schmidt
- Subjects
0103 physical sciences ,Physical and Theoretical Chemistry ,010402 general chemistry ,010303 astronomy & astrophysics ,01 natural sciences ,0104 chemical sciences - Abstract
Polycyclic aromatic hydrocarbons (PAHs) are intermediates in the formation of soot particles and interstellar grains. However, their formation mechanisms in combustion and interstellar environments are not fully understood. The production of tricyclic PAHs and, in particular, the conversion of a PAH containing a five-membered ring to one with a six-membered ring are of interest to explain PAH abundances in combustion processes. In the present work, resonant ionization mass spectrometry in conjunction with isotopic labeling is used to investigate the formation of the phenalenyl radical from acenaphthylene and methane in an electrical discharge. We show that in this environment the CH cycloaddition mechanism converts a five-membered ring to a six-membered ring. This mechanism can occur in tandem with other PAH formation mechanisms such as hydrogen abstraction/acetylene addition (HACA) to produce larger PAHs in flames and the interstellar medium.
- Published
- 2021
3. POPTARTS: A New Method to Determine Quantum Yields in a Molecular Beam
- Author
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Jyoti S. Campbell, Klaas Nauta, Christopher S. Hansen, and Scott H. Kable
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Physical and Theoretical Chemistry - Abstract
A new technique is reported to determine absolute photodissociation quantum yields, ϕ
- Published
- 2022
4. CO FORMATION FROM ACETONE PHOTOLYSIS: THE ROAMING PATHWAY
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Lorrie Jacob, Scott Kable, Klaas Nauta, Timothy Schmidt, and Kelvin Lee
- Published
- 2022
5. Diabatic Valence-Hole States in the C
- Author
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Jun, Jiang, Hong-Zhou, Ye, Klaas, Nauta, Troy, Van Voorhis, Timothy W, Schmidt, and Robert W, Field
- Abstract
Despite the long history of spectroscopic studies of the C
- Published
- 2022
6. Diabatic valence-hole states in the C$_2$ molecule: 'Putting Humpty Dumpty together again'
- Author
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Jun Jiang, Hong-Zhou Ye, Klaas Nauta, Troy Van Voorhis, Timothy W. Schmidt, and Robert W. Field
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Chemical Physics (physics.chem-ph) ,Physics - Chemical Physics ,FOS: Physical sciences ,Physical and Theoretical Chemistry - Abstract
Despite the long history of spectroscopic studies of the C$_2$ molecule, fundamental questions about its chemical bonding are still being hotly debated. The complex electronic structure of C$_2$ is a consequence of its dense manifold of near-degenerate, low-lying electronic states. A global multi-state diabatic model is proposed here to disentangle the numerous configuration interactions within four symmetry manifolds of C$_2$ ($^{1}\Pi_g$, $^{3}\Pi_g$, $^{1}\Sigma_u^+$, and $^{3}\Sigma_u^+$). The key concept of our model is the existence of two "valence-hole" configurations, $2\sigma_g^22\sigma_u^11\pi_{u}^33\sigma_g^2$ for $^{1,3}\Pi_g$ states and $2\sigma_g^22\sigma_u^11\pi_{u}^43\sigma_g^1$ for $^{1,3}\Sigma_u^+$ states that derive from $3\sigma_g\leftarrow2\sigma_u$ electron promotion. The lowest-energy state from each of the four C$_2$ symmetry species is dominated by this type of valence-hole configuration at its equilibrium internuclear separation. As a result of their large binding energy (nominal bond order of 3) and correlation with the 2s$^2$2p$^2$+2s2p$^3$ separated-atom configurations, the presence of these valence-hole configurations has a profound impact on the $global$ electronic structure and unimolecular dynamics of C$_2$.
- Published
- 2022
- Full Text
- View/download PDF
7. Rotational resonances in the H 2 CO roaming reaction are revealed by detailed correlations
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Mitchell S. Quinn, Joel M. Bowman, Paul L. Houston, Klaas Nauta, Scott H. Kable, and Meredith J. T. Jordan
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Multidisciplinary ,010304 chemical physics ,Hydrogen molecule ,Photodissociation ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical physics ,Quantum state ,0103 physical sciences ,Potential energy surface ,Roaming ,Carbon monoxide - Abstract
Duality of roaming mechanism in H 2 CO The phenomenon of roaming in chemical reactions (that is, bypassing the minimum energy pathway from unlikely geometries) has attracted a great deal of attention in the chemical reaction dynamics community over the past decade and still demonstrates unexpected results. Using velocity-map imaging of state-selected H 2 products of H 2 CO photodissociation, Quinn et al. discovered the bimodal structure of rotational distribution of the other product fragment, CO. Quasiclassical trajectories showed that this bimodality originates from two distinctive reaction pathways that proceed by the trans or cis configuration of O–C–H⋯H, leading to high or low rotational excitations of CO, respectively. Whether such a mechanism is present in the many other chemical reactions for which roaming reaction pathways have been reported is yet to be determined. Science , this issue p. 1592
- Published
- 2020
8. Photodissociation of dicarbon: How nature breaks an unusual multiple bond
- Author
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Jasmin Borsovszky, Klaas Nauta, Jun Jiang, Christopher S. Hansen, Laura K. McKemmish, Robert W. Field, John F. Stanton, Scott H. Kable, and Timothy W. Schmidt
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Multidisciplinary ,Social Sciences ,photodissociation ,comets ,dicarbon - Abstract
Significance It has long been observed that the coma of a comet is often green while its tail is not. While the explanation for this must be that the molecules responsible for the green emission, C2, are photodissociated, the mechanism was, until now, unknown. We have observed the photodissociation of C2 in the laboratory for the first time and, in doing so, have determined its bond dissociation energy with unprecedented precision. Invoking the observed mechanism, the calculated lifetime of cometary C2 is found to be consistent with astronomical observations., The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2. From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ·mol−1 is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ·mol−1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions.
- Published
- 2021
9. Photodissociation dynamics of CF
- Author
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Jyoti S, Campbell, Klaas, Nauta, Scott H, Kable, and Christopher S, Hansen
- Abstract
The photodissociation dynamics of jet-cooled trifluoroacetaldehyde (CF
- Published
- 2021
10. PAH growth in flames and space: Formation of phenalenyl radical
- Author
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Zachariah Levey, Benjamin Laws, Srivathsan Sundar, Klaas Nauta, Scott Kable, Gabriel da Silva, John Stanton, and Timothy Schmidt
- Abstract
Polycyclic aromatic hydrocarbons (PAHs) are intermediates in the formation of soot particles and interstellar grains. However, their formation mechanisms in combustion and interstellar environments are not fully understood. The production of tricyclic PAHs and, in particular, the conversion of a PAH containing a five-membered ring to one with a six-membered ring is of interest to explain PAH abundances in combustion processes. In the present work, resonant ionization mass spectrometry in conjunction with isotopic labelling is used to investigate the formation of the phenalenyl radical from acenaphthylene and methane in an electrical discharge. We show that in this environment, the CH cycloaddition mechanism converts a five-membered ring to a six-membered ring. This mechanism can occur in tandem with other PAH formation mechanisms such as hydrogen abstraction/ acetylene addition (HACA) to produce larger PAHs in flames and the interstellar medium.
- Published
- 2021
11. PAH growth in flames and space: Formation of phenalenyl radical
- Author
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Klaas Nauta, Scott H. Kable, Srivathsan P. Sundar, Gabriel da Silva, Timothy W. Schmidt, Zachariah D. Levey, John F. Stanton, and Benjamin A. Laws
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Interstellar medium ,chemistry.chemical_compound ,Acetylene ,Chemistry ,medicine ,Combustion ,Hydrogen atom abstraction ,medicine.disease_cause ,Ring (chemistry) ,Photochemistry ,Acenaphthylene ,Methane ,Soot - Abstract
Polycyclic aromatic hydrocarbons (PAHs) are intermediates in the formation of soot particles and interstellar grains. However, their formation mechanisms in combustion and interstellar environments are not fully understood. The production of tricyclic PAHs and, in particular, the conversion of a PAH containing a five-membered ring to one with a six-membered ring is of interest to explain PAH abundances in combustion processes. In the present work, resonant ionization mass spectrometry in conjunction with isotopic labelling is used to investigate the formation of the phenalenyl radical from acenaphthylene and methane in an electrical discharge. We show that in this environment, the CH cycloaddition mechanism converts a five-membered ring to a six-membered ring. This mechanism can occur in tandem with other PAH formation mechanisms such as hydrogen abstraction/ acetylene addition (HACA) to produce larger PAHs in flames and the interstellar medium.
- Published
- 2021
12. VALENCE-HOLE ELECTRON CONFIGURATIONS: A NEW GLOBAL ELECTRONIC STRUCTURE PARADIGM FOR C2 AND BEYOND
- Author
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Timothy W. Schmidt, Klaas Nauta, Jun Jiang, and Robert Field
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Physics ,Valence (chemistry) ,Condensed matter physics ,Electron configuration ,Electronic structure - Published
- 2021
13. Quantum-Induced Symmetry Breaking in the Deuterated Dihydroanthracenyl Radical
- Author
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Timothy W. Schmidt, Scott H. Kable, Callan M. Wilcox, Klaas Nauta, and Olha Krechkivska
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010304 chemical physics ,Chemistry ,010402 general chemistry ,Mass spectrometry ,01 natural sciences ,Molecular physics ,Spectral line ,0104 chemical sciences ,Deuterium ,0103 physical sciences ,Density functional theory ,Isotopologue ,Symmetry breaking ,Physical and Theoretical Chemistry ,Ionization energy ,Spectroscopy - Abstract
The hydrogen-atom adduct with anthracene, 9-dihydroanthracenyl radical (C14H11), and its deuterated analogue have been identified by laser spectroscopy coupled to time-of-flight mass spectrometry, supported by time-dependent density functional theory calculations. The electronic spectrum of 9-dihydroanthracenyl radical exhibits an origin band at 19115 cm-1 and its ionization energy was determined to be 6.346(1) eV. The spectra reveal a low-frequency vibrational progression corresponding to a mode described by a butterfly inversion. In the deuterated analogue, a zero-point-energy imbalance along this coordinate is found to lead to a doubling of the observed spectral lines in the progression. This is attributed to quantum-induced symmetry breaking as previously observed in isotopologues of CH5+.
- Published
- 2019
14. Dynamics and quantum yields of H2 + CH2CO as a primary photolysis channel in CH3CHO
- Author
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Alireza Kharazmi, Aaron W. Harrison, Meredith J. T. Jordan, Scott H. Kable, Keiran N Rowell, Klaas Nauta, Kin Long Kelvin Lee, Mitchell S. Quinn, and Miranda F. Shaw
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Materials science ,Hydrogen ,Photodissociation ,General Physics and Astronomy ,Quantum yield ,Infrared spectroscopy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Molecular physics ,3. Good health ,0104 chemical sciences ,Ion ,chemistry ,Ionization ,Physical and Theoretical Chemistry ,Fourier transform infrared spectroscopy ,0210 nano-technology ,Molecular beam - Abstract
The first experimental observation of the primary photochemical channel of acetaldehyde leading to the formation of ketene (CH2CO) and hydrogen (H2) molecular products is reported. Acetaldehyde (CH3CHO) was photolysed in a molecular beam at 305.6 nm and the resulting H2 product characterized using velocity-map ion (VMI) imaging. Resonance-enhanced multiphoton ionization (REMPI), via two-photon excitation to the double-well EF 1Σ+g state, was used to state-selectively ionize the H2 and determine angular momentum distributions for H2 (ν = 0) and H2 (ν = 1). Velocity-map ion images were obtained for H2 (ν = 0 and 1, J = 5), allowing the total translational energy release of the photodissociation process to be determined. Following photolysis of CH3CHO in a gas cell, the CH2CO co-fragment was identified, using Fourier transform infrared spectroscopy, by its characteristic infrared absorption at 2150 cm−1. The measured quantum yield of the CH2CO + H2 product channel at 305.0 nm is ϕ = 0.0075 ± 0.0025 for both 15 Torr of neat CH3CHO and a mixture with 745 Torr of N2. Although small, this result has implications for the atmospheric photochemistry of carbonyls and this reaction represents a new tropospheric source of H2. Quasi-classical trajectory (QCT) simulations on a zero-point energy corrected reaction-path potential are also performed. The experimental REMPI and VMI image distributions are not consistent with the QCT simulations, indicating a non reaction-path mechanism should be considered.
- Published
- 2019
15. Disentangling the H2E, F(1Σg+) (v′=0−18)←X(1Σg+)(v″=3−9)(2+1) REMPI spectrum via 2D velocity-mapped imaging
- Author
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Mitchell S. Quinn, Scott H. Kable, and Klaas Nauta
- Subjects
010304 chemical physics ,Spectrum (functional analysis) ,Photodissociation ,Hydrogen molecule ,Biophysics ,Formaldehyde ,Analytical chemistry ,010402 general chemistry ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Ionization ,0103 physical sciences ,Physical and Theoretical Chemistry ,Molecular Biology - Abstract
We have measured the two-photon EF←X (v″=3−9) Resonance-Enhanced Multiphoton Ionization (REMPI) spectrum of H2 by producing the hydrogen molecule via photolysis of H2CO. H2 is produced with rovibrational energies up to 30,000 cm−1, at a maximum observed (v″,J″) of (9,5). In the well-resolved jet-cooled H2CO spectrum, ortho and para H2 are selectively produced with near 100% selectivity. Over 470 REMPI transitions were identified in the EF−X band system, many of which have not been seen previously, including transitions to EF levels not yet accurately measured. Speed distributions were obtained for each REMPI transition using Velocity-mapped imaging, aiding in the assignment by providing a precise measurement of the internal energy of the H2 molecule.
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- 2021
- Full Text
- View/download PDF
16. The dynamics of CO production from the photolysis of acetone across the whole S1 ← S0 absorption spectrum: Roaming and triple fragmentation pathways
- Author
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Kin Long Kelvin Lee, Klaas Nauta, Timothy Schmidt, Lorrie S.D. Jacob, and Scott Kable
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General Physics and Astronomy ,Physical and Theoretical Chemistry - Abstract
The unimolecular photodissociation dynamics of acetone spanning the entire S1 ← S0 absorption spectrum have been reinvestigated, with a focus on mechanisms that produce CO. At excitation wavelengths of λ > 305.8 nm, all photoproducts are formed on the S0 state after internal conversion. A roaming mechanism forming C2H6 + CO is active in the window λ = 311.2–305.8 nm. From λ = 305.8 to 262 nm, little or no CO is produced with the photochemistry dominated by the Norrish-type I C–C bond cleavage on the lowest excited triplet state, T1. At higher energy ( λ < 262 nm), an increasing fraction of CH3CO radicals from the primary reaction have sufficient internal energy to spontaneously decompose to CH3 + CO. A new model is presented to account for the kinetic energy distribution of the secondary CH3 radical, allowing us to determine the height of the energetic barrier to CH3CO decomposition as 68 ± 4 kJ mol−1, which lies midway between previous measurements. The fraction of CO from triple fragmentation rises smoothly from 260 to 248 nm. We see no evidence of the return of roaming, or any other S0 reaction, in this higher energy region of the first electronic absorption band.
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- 2022
17. Aliphatic hydrocarbon content of the interstellar dust
- Author
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Scott H. Kable, O. Krechkivska, Aditya Rawal, Michael G. Burton, Klaas Nauta, Melike Afşar, B. Günay, and Timothy W. Schmidt
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Astrochemistry ,010504 meteorology & atmospheric sciences ,Extinction (astronomy) ,Analytical chemistry ,chemistry.chemical_element ,FOS: Physical sciences ,01 natural sciences ,Spectral line ,0103 physical sciences ,Optical depth (astrophysics) ,Physics::Chemical Physics ,Absorption (electromagnetic radiation) ,010303 astronomy & astrophysics ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences ,Cosmic dust ,Physics ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Interstellar medium ,chemistry ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics - Instrumentation and Methods for Astrophysics ,Carbon - Abstract
In the interstellar medium, carbon is distributed between the gas and solid phases. However, while about half of the expected carbon abundance can be accounted for in the gas phase, there is considerable uncertainty as to the amount incorporated in interstellar dust. The aliphatic component of the carbonaceous dust is of particular interest because it produces a significant 3.4 $\mu$m absorption feature when viewed against a background radiation source. The optical depth of the 3.4 $\mu$m absorption feature is related to the number of aliphatic carbon C-H bonds along the line of sight. It is possible to estimate the column density of carbon locked up in the aliphatic hydrocarbon component of interstellar dust from quantitative analysis of the 3.4 $\mu$m interstellar absorption feature providing that the absorption coefficient of aliphatic hydrocarbons incorporated in the interstellar dust is known. We generated laboratory analogues of interstellar dust by experimentally mimicking interstellar/circumstellar conditions. The resultant spectra of these dust analogues closely match those from astronomical observations. The measurements of the absorption coefficient of aliphatic hydrocarbons incorporated in the analogues were carried out by a procedure which combined FTIR and $^{13}$C NMR spectroscopies. The absorption coefficients obtained for both interstellar analogues were found to be in close agreement (4.76(8) $\times$ 10$^{-18}$ cm group$^{-1}$ and 4.69(14) $\times$ 10$^{-18}$ cm group$^{-1}$), less than half those obtained in studies using small aliphatic molecules. The results thus obtained permit direct calibration of the astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the interstellar medium.
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- 2020
- Full Text
- View/download PDF
18. Higher vibrational levels of the D1Σu+ state of dicarbon: New Mulliken bands
- Author
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Klaas Nauta, O. Krechkivska, Scott H. Kable, Timothy W. Schmidt, B. A. Welsh, and J.N. Fréreux
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Physics ,010304 chemical physics ,State (functional analysis) ,010402 general chemistry ,01 natural sciences ,Diatomic molecule ,Fluorescence ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Bond length ,Crystallography ,0103 physical sciences ,Physical and Theoretical Chemistry ,Atomic physics ,Spectroscopy ,Sequence (medicine) - Abstract
The Δ v = + 2 sequence of the Mulliken system of C 2 is reported for the first time. Seven new levels of the D 1 Σ u + state of C 2 , v = 5 through v = 11 , were found. The analysis reveals the rotational constants and origin of each band. The numbers are combined with the data reported for previously reported levels, v = 0 through v = 4 , to generate updated Dunham parameters for the D 1 Σ u + state: ω e = 1829.905 ( 57 ) cm −1 , ω e x e = 14.089 ( 8 ) cm −1 , ω e y e = 0 cm −1 , ω e z e = 0.00124 ( 3 ) cm −1 , B e = 1.83254 ( 46 ) cm −1 , α e = 0.01909 ( 18 ) cm −1 and β e = - 7.28 ( 14 ) × 10 - 5 cm −1 . The determined equilibrium bond length R e = 1.23804 ( 28 ) A. The fluorescence lifetimes of the new levels are also reported.
- Published
- 2018
19. Photodissociation dynamics of CF3CHO: C–C bond cleavage
- Author
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Scott H. Kable, Klaas Nauta, Christopher S. Hansen, and Jyoti S. Campbell
- Subjects
Materials science ,010304 chemical physics ,Absorption spectroscopy ,Photodissociation ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Internal conversion (chemistry) ,01 natural sciences ,7. Clean energy ,Molecular physics ,Dissociation (chemistry) ,Ion ,Intersystem crossing ,Excited state ,0103 physical sciences ,Physical and Theoretical Chemistry ,Triplet state ,0210 nano-technology - Abstract
The photodissociation dynamics of jet-cooled trifluoroacetaldehyde (CF3CHO) into radical products, CF3 + HCO, was explored using velocity mapped ion imaging over the wavelength range 297.5 nm [Formula: see text] 342.8 nm (33 613–29 172 cm−1) covering the entire section of the absorption spectrum accessible with solar actinic wavelengths at the ground level. After initial excitation to the first excited singlet state, S1, the radical dissociation proceeds largely via the first excited triplet state, T1, at excitation energies above the T1 barrier. By combining velocity-mapped ion imaging with high-level theory, we place this barrier at 368.3 ± 2.4 kJ mol−1 (30 780 ± 200 cm−1). After exciting to S1 at energies below this barrier, the dissociation proceeds exclusively via the ground electronic state, S0. The dissociation threshold is determined to be 335.7 ± 1.8 kJ mol−1 (28 060 ± 150 cm−1). Using laser-induced fluorescence spectroscopy, the origin of the S1 ← S0 transition is assigned at 28 903 cm−1. The S0 dissociation channel is active at the S1 origin, but the yield significantly increases above 29 100 cm−1 due to enhanced intersystem crossing or internal conversion.
- Published
- 2021
20. General hospital specialists’ attitudes toward psychiatry: a cross-sectional survey in seven countries
- Author
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Victoria de Carvalho Pereira, Jane McCarthy, David B Menkes, Alexander Kursakov, Birit F P Broekman, Doron Amsalem, Xiaoping Wang, Klaas Nauta, Alexander Merkin, Jun Wang, Clarissa de Rosalmeida Dantas, I Wimalaratne, Anuprabha Wickramasinghe, Raz Gross, S.T. Kathriarachchi, Psychiatry, APH - Mental Health, Public and occupational health, Hematology laboratory, and VU University medical center
- Subjects
Male ,medicine.medical_specialty ,Referral ,Attitude of Health Personnel ,Cross-sectional study ,health services administration & management ,Specialty ,Hospitals, General ,Affect (psychology) ,General Practitioners ,Surveys and Questionnaires ,Acute care ,medicine ,Humans ,Seniority ,Psychiatry ,Chronic care ,business.industry ,General Medicine ,education & training (see medical education & training) ,Mental Health ,Cross-Sectional Studies ,Medicine ,Female ,Descriptive research ,business - Abstract
ObjectivePsychiatric comorbidities are common in physical illness and significantly affect health outcomes. Attitudes of general hospital doctors toward psychiatry are important as they influence referral patterns and quality of care. Little is known about these attitudes and their cultural correlates. The aim of this study was to identify attitudes toward psychiatry among general hospital specialists in relation to culture of the practice setting and other clinician factors (gender, age, seniority and specialty).MethodsA cross-sectional, descriptive study was carried out in seven countries (New Zealand, China, Sri Lanka, Russia, Israel, Brazil, the Netherlands). Data were collected from senior medical staff of various disciplines using an updated version of Mayou and Smith’s (1986) self-administered questionnaire.ResultsA total of 889 hospital doctors participated. While favourable attitudes toward both psychiatric consultation and management were endorsed by a majority, significant differences were also observed between countries. Subgroup differences were mostly confined to gender, acuity of practice setting and specialty. For example, female doctors in Russia (χ2=7.7, p=0.0056), China (χ2=9.2, p=0.0025) and the Netherlands (χ2=5.7, p=0.0174) endorsed more positive attitudes compared with their male counterparts, but this gender effect was not replicated in the total sample. Chronic care specialists were overall more inclined to manage patients’ emotional problems compared with those working in acute care (χ2=70.8, p (adjusted)ConclusionsThis study adds to evidence for the association of medical attitudes with individual clinician factors and demonstrates that the influence of these factors varies by country. Understanding these issues may help to overcome barriers and improve quality of care provided to general hospital patients.
- Published
- 2021
21. Quantum-Induced Symmetry-Breaking in the Deuterated Dihydroanthracenyl Radical
- Author
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Olha Krechkivska, Scott H. Kable, Callan M. Wilcox, Timothy W. Schmidt, and Klaas Nauta
- Subjects
Materials science ,Deuterium ,Kinetic isotope effect ,Density functional theory ,Symmetry breaking ,Ionization energy ,Spectroscopy ,Mass spectrometry ,Molecular physics ,Spectral line - Abstract
The hydrogen-atom adduct with anthracene, 9-dihydroanthracenyl radical (C14H11), and its deuterated analogue, have been identified by laser spectroscopy coupled to time-of-flight mass spectrometry, supported by time-dependent density functional theory calculations. The electronic spectrum of 9-dihydroanthracenyl radical exhibits an origin band at 19115 cm-1 and its ionization energy was determined to be 6.346(1) eV. The spectra reveal a low-frequency vibrational progression corresponding to a mode described by a butterfly-inversion. In the deuterated analogue, a zero-point-energy imbalance along this coordinate is found to lead to a doubling of the observed spectral lines in the progression. This is attributed to quantum-induced symmetry breaking as previously observed in isotopologues of CH5+.
- Published
- 2019
22. Quantum-Induced Symmetry-Breaking in the Deuterated Dihydroanthracenyl Radical
- Author
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Timothy Schmidt, Scott Kable, Klaas Nauta, Callan Wilcox, and Olha Krechkivska
- Abstract
The hydrogen-atom adduct with anthracene, 9-dihydroanthracenyl radical (C14H11), and its deuterated analogue, have been identified by laser spectroscopy coupled to time-of-flight mass spectrometry, supported by time-dependent density functional theory calculations. The electronic spectrum of 9-dihydroanthracenyl radical exhibits an origin band at 19115 cm-1 and its ionization energy was determined to be 6.346(1) eV. The spectra reveal a low-frequency vibrational progression corresponding to a mode described by a butterfly-inversion. In the deuterated analogue, a zero-point-energy imbalance along this coordinate is found to lead to a doubling of the observed spectral lines in the progression. This is attributed to quantum-induced symmetry breaking as previously observed in isotopologues of CH5+.
- Published
- 2019
23. Dynamics and quantum yields of H
- Author
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Aaron W, Harrison, Alireza, Kharazmi, Miranda F, Shaw, Mitchell S, Quinn, K L Kelvin, Lee, Klaas, Nauta, Keiran N, Rowell, Meredith J T, Jordan, and Scott H, Kable
- Abstract
The first experimental observation of the primary photochemical channel of acetaldehyde leading to the formation of ketene (CH
- Published
- 2019
24. Jet-Cooled Spectroscopy of ortho-Hydroxycyclohexadienyl Radicals
- Author
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Callan M. Wilcox, Scott H. Kable, O. Krechkivska, Klaas Nauta, and Timothy W. Schmidt
- Subjects
010304 chemical physics ,Chemistry ,010402 general chemistry ,Ring (chemistry) ,01 natural sciences ,Spectral line ,0104 chemical sciences ,Ab initio quantum chemistry methods ,Ionization ,Excited state ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,Physical chemistry ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Spectroscopy ,Ground state ,Conformational isomerism - Abstract
The electronic spectra of the ortho-hydroxycyclohexadienyl radical have been observed following the supersonic expansion of the electric discharge products of phenol and water. Hydrogen atoms, split from water, add to the phenol ring at the ortho position, generating syn and anti rotamers with respect to the hydroxyl group. The D1 ← D0 transitions were recorded by resonance-enhanced multiphoton ionization spectroscopy. The spectrum of each isomer was isolated through hole-burning spectroscopy. The assignment and symmetry of the excited state are evaluated through ab initio calculations and are employed to assign each spectrum. Both rotamers are calculated to have a puckered ring in the excited state, leading to C1 symmetry. The spectrum of the anti isomer is assigned well using this symmetry; however, the syn isomer is assigned better in the Cs symmetry of the ground state. We use Duschinsky matrices as a tool for the spectroscopist to determine which point group to use when ab initio calculations are amb...
- Published
- 2018
25. Hydrogen-atom attack on phenol and toluene is ortho-directed
- Author
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Callan M. Wilcox, Bun Chan, O. Krechkivska, Scott A. Reid, Scott H. Kable, Klaas Nauta, Leo Radom, Rebecca Jacob, Timothy W. Schmidt, and Tyler P. Troy
- Subjects
010304 chemical physics ,Stereochemistry ,Radical ,General Physics and Astronomy ,Hydrogen atom ,010402 general chemistry ,Resonance (chemistry) ,01 natural sciences ,7. Clean energy ,Toluene ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Ionization ,0103 physical sciences ,Physical chemistry ,Physical and Theoretical Chemistry ,Ionization energy ,Benzene ,Conformational isomerism - Abstract
The reaction of H + phenol and H/D + toluene has been studied in a supersonic expansion after electric discharge. The (1 + 1') resonance-enhanced multiphoton ionization (REMPI) spectra of the reaction products, at m/z = parent + 1, or parent + 2 amu, were measured by scanning the first (resonance) laser. The resulting spectra are highly structured. Ionization energies were measured by scanning the second (ionization) laser, while the first laser was tuned to a specific transition. Theoretical calculations, benchmarked to the well-studied H + benzene → cyclohexadienyl radical reaction, were performed. The spectrum arising from the reaction of H + phenol is attributed solely to the ortho-hydroxy-cyclohexadienyl radical, which was found in two conformers (syn and anti). Similarly, the reaction of H/D + toluene formed solely the ortho isomer. The preference for the ortho isomer at 100-200 K in the molecular beam is attributed to kinetic, not thermodynamic effects, caused by an entrance channel barrier that is ∼5 kJ mol(-1) lower for ortho than for other isomers. Based on these results, we predict that the reaction of H + phenol and H + toluene should still favour the ortho isomer under elevated temperature conditions in the early stages of combustion (200-400 °C).
- Published
- 2016
26. Interconversion of Methyltropyl and Xylyl Radicals: A Pathway Unavailable to the Benzyl-Tropyl Rearrangement
- Author
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Timothy W. Schmidt, Callan M. Wilcox, Klaas Nauta, Gabriel da Silva, Tyler P. Troy, Neil J. Reilly, Zijun Ge, Scott H. Kable, Michael C. McCarthy, and Damian L. Kokkin
- Subjects
010304 chemical physics ,Radical ,Infrared spectroscopy ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Toluene ,0104 chemical sciences ,Styrene ,chemistry.chemical_compound ,chemistry ,Ionization ,0103 physical sciences ,Electric discharge ,Physical and Theoretical Chemistry ,Benzene ,Isomerization - Abstract
The products of an electrical discharge containing toluene are interrogated using resonance-enhanced multiphoton ionization and laser-induced fluorescence spectroscopies. A previously unreported electronic spectrum recorded at m/z = 105, with a putative origin band at 26053 cm–1, is assigned to methyltropyl radical, which appears to be a major product of the toluene discharge, plausibly arising from CH insertion. All three o-, m-, and p-xylyl isomers are also identified. These isomers are detected in electrical discharges containing various xylenes, where it is also found that interconversion occurs: A discharge of o-xylene produces some m-xylyl; a discharge of m-xylene produces some o-xylyl; and a discharge of p-xylene produces all three isomers. No α-methylbenzyl was detected, but styrene was. These observations are supported by state-of-the-art quantum chemical calculations, which reveal an isomerization pathway between methyltropyl and xylyl radicals for which there is no analogue in the canonical tro...
- Published
- 2018
27. Resonance-Enhanced 2-Photon Ionization Scheme for C2 through a Newly Identified Band System: 43Πg–a3Πu
- Author
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Timothy W. Schmidt, George B. Bacskay, Scott H. Kable, Klaas Nauta, Thomas D. Kreuscher, O. Krechkivska, and Tyler P. Troy
- Subjects
010304 chemical physics ,Chemistry ,Overtone band ,01 natural sciences ,Hot band ,Bond length ,Ionization ,Molecular vibration ,0103 physical sciences ,Single bond ,Rotational spectroscopy ,Physical and Theoretical Chemistry ,Atomic physics ,Spectroscopy ,010303 astronomy & astrophysics - Abstract
We report the observation of a new band system of C2, namely, the 4(3)Πg-a(3)Πu system. The bands, observed by resonant 2-photon ionization spectroscopy and time-of-flight mass spectrometry, were identified through a synergy of high-level ab initio computation and double-resonance spectroscopy. Two bands are firmly identified, 1-3 and 0-2, allowing the 4(3)Πg origin to be placed at 51496.44 cm(-1). The 4(3)Πg state is characterized as having a single bond, with a vibrational frequency of about 1268 cm(-1), and an equilibrium bond length of 1.57 Å. The state is predicted to exhibit a barrier to dissociation, with a rotational constant that unusually increases with vibrational excitation up to a maximum before decreasing at higher vibrational excitation. The new band system allows us to probe the a(3)Πu state of C2 through a straightforward 1 + 1 REMPI scheme.
- Published
- 2015
28. H and D Attachment to Naphthalene: Spectra and Thermochemistry of Cold Gas-Phase 1-C10H9 and 1-C10H8D Radicals and Cations
- Author
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Yu Liu, Rebecca Jacob, Callan M. Wilcox, Scott H. Kable, Timothy W. Schmidt, Klaas Nauta, Bun Chan, O. Krechkivska, and Leo Radom
- Subjects
Proton ,Chemistry ,Radical ,Mass spectrometry ,7. Clean energy ,Bond-dissociation energy ,Physics::Atomic and Molecular Clusters ,Thermochemistry ,Physical chemistry ,Density functional theory ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Spectroscopy - Abstract
Excitation spectra of the 1H-naphthalene (1-C10H9) and 1D-naphthalene (1-C10H8D) radicals, and their cations, are obtained by laser spectroscopy and mass spectrometry of a skimmed free-jet expansion following an electrical discharge. The spectra are assigned on the basis of density functional theory calculations. Isotopic shifts in origin transitions, vibrational frequencies and ionization energies were found to be well reproduced by (time-dependent) density functional theory. Absolute bond dissociation energies, ionization energies and proton affinities were calculated using high-level quantum chemical methods.
- Published
- 2015
29. Atmospheric oxidation intermediates: Laser spectroscopy of resonance-stabilized radicals from p-cymene
- Author
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Tyler P. Troy, Timothy W. Schmidt, Murad J. Y. Tayebjee, Klaas Nauta, and Scott H. Kable
- Subjects
p-Cymene ,Chemistry ,Radical ,Monoterpene ,Analytical chemistry ,General Physics and Astronomy ,Hydrogen atom ,Chromophore ,Photochemistry ,Resonance (chemistry) ,chemistry.chemical_compound ,Physical and Theoretical Chemistry ,Spectroscopy ,Methyl group - Abstract
Several resonance-stabilized radicals are observed as products of an electrical discharge containing p -cymene, a biogenic monoterpene that contributes to secondary organic aerosols after atmospheric oxidation. Three radicals are identified by resonant 2-color 2-photon ionization mass spectrometry, corresponding to loss of a methyl group or hydrogen atom from the parent p -cymene structure. The radicals are found to absorb in the spectral region consistent with a benzylic chromophore. The spectrum observed on m / z 119 is assigned to α ,4-dimethylbenzyl radical, and those on m / z 133 to the α , α ,4-trimethylbenzyl and p -isopropylbenzyl radicals, the latter two being intermediates in the atmospheric oxidation of p -cymene.
- Published
- 2015
30. The energy dependence of CO(v,J) produced from H
- Author
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Mitchell S, Quinn, Duncan U, Andrews, Klaas, Nauta, Meredith J T, Jordan, and Scott H, Kable
- Abstract
The dynamics of CO production from photolysis of H
- Published
- 2017
31. Photodissociation of acetone from 266 to 312 nm: Dynamics of CH
- Author
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Kin Long Kelvin, Lee, Klaas, Nauta, and Scott H, Kable
- Abstract
The photodissociation dynamics of acetone (CH
- Published
- 2017
32. Two roaming pathways in the photolysis of CH3CHO between 328 and 308 nm
- Author
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Meredith J. T. Jordan, Scott A. Reid, Kin Long Kelvin Lee, Alan T. Maccarone, Mitchell S. Quinn, Klaas Nauta, Scott H. Kable, and Paul L. Houston
- Subjects
Wavelength ,Range (particle radiation) ,Component (thermodynamics) ,Chemistry ,Real-time computing ,Photodissociation ,General Chemistry ,Roaming ,Molecular physics ,Chemical reaction ,Bond cleavage ,Rotational energy - Abstract
The correlated speed and rotational energy distributions of the CO fragment from photodissociation of CH3CHO have been measured at a range of wavelengths from 308 to 328 nm. The distributions are bimodal, showing low J, slow speed, and high J, fast speed components. The cold component disappears for λ > 325 nm. This threshold corresponds to C–H bond cleavage and we assign these CO products as arising from roaming of a H-atom about a CH3CO core. We attribute the hot component to CO formed through CH3-roaming. No evidence was observed for the presence of a transition state mechanism. This is the first time two distinct roaming channels have been observed from the same electronic state. The results support the growing understanding that roaming can be significant in chemical reactions and outweigh traditional pathways.
- Published
- 2014
33. Excitation Spectra of Large Jet-Cooled Polycyclic Aromatic Hydrocarbon Radicals: 9-Anthracenylmethyl (C15H11) and 1-Pyrenylmethyl (C17H11)
- Author
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Tyler P. Troy, Gabrielle V. G. Woodhouse, Timothy W. Schmidt, Klaas Nauta, Gerard D. O’Connor, and George B. Bacskay
- Subjects
Wavelength ,Chemistry ,Radical ,Excited state ,Molecule ,Emission spectrum ,Physical and Theoretical Chemistry ,Atomic physics ,Chromophore ,Absorption (electromagnetic radiation) ,Spectroscopy - Abstract
The 9-anthracenylmethyl (C15H11) and 1-pyrenylmethyl (C17H11) radicals were identified by a combination of mass-resolved laser spectroscopy of a jet-cooled electrical discharge and quantum chemical methods. The 9-anthracenylmethyl radical was found to exhibit an origin band at 13757 cm(-1), with vibrational structure observed in a1 modes, and even quanta of b1 and a2 modes. The 1-pyrenylmethyl radical was found to exhibit an origin band at 13,417 cm(-1), with a more complex vibrational structure as compared to 9-anthracenylmethyl, on account of its lower symmetry and larger size. The origin bands of these species were predicted to within 250 cm(-1) by fitting a linear relationship between observed origin wavelengths of similar chromophores and the calculated TD-B3LYP transition energies. A refined fit including the title radicals provides estimated absorption energies for the larger 2-perylenylmethyl and 6-anthanthrenylmethyl species of 1.44 and 1.41 eV, respectively, with an estimated error of 30 meV.
- Published
- 2013
34. Electronic spectroscopy of the transition of DCO and lifetimes and relative quantum yields of the state
- Author
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Klaas Nauta, Steven J. Rowling, Scott H. Kable, and Scott A. Reid
- Subjects
Coupling constant ,Materials science ,Transition dipole moment ,Photodissociation ,Electron spectroscopy ,Atomic and Molecular Physics, and Optics ,Spectral line ,Nuclear magnetic resonance ,Excited state ,Physical and Theoretical Chemistry ,Atomic physics ,Laser-induced fluorescence ,Astrophysics::Galaxy Astrophysics ,Spectroscopy ,Excitation - Abstract
We have measured the laser induced fluorescence excitation spectrum of the origin of the DCO B ∼ ( 2 A ′ ) ← X ∼ ( 2 A ′ ) transition under a variety of experimental conditions, ranging from cooled to 7 K in a supersonic jet, to nascent in the photolysis of D2CO. By analysing successively more complex spectra we have derived rotational, centrifugal distortion, and spin-rotation coupling constants that provided the best fit to the experimental frequencies. Fluorescence lifetimes were measured for 35 rotationally-resolved excited states, which provided relative quantum yields for these states. Unlike HCO, the lifetimes showed only a weak dependence on N and Ka, evincing a weaker coupling between the A ∼ and B ∼ states in DCO than HCO. Intensity ratios for pairs of transitions with the same lower state were used to extract the transition moment angle, θ = 44.6 ± 2.5° and the axis switching angle, ϕ = 3.1 ± 0.5° for the B ∼ – X ∼ transition. Both angles are consistent with the expected change upon deuteration of HCO.
- Published
- 2011
35. Excitation and Emission Spectra of Jet-Cooled Naphthylmethyl Radicals
- Author
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Bligh A. Gibson, Rob Sharp, Klaas Nauta, Tyler P. Troy, Masakazu Nakajima, Nahid Chalyavi, Scott H. Kable, and Timothy W. Schmidt
- Subjects
Extraterrestrial Environment ,Free Radicals ,Chemistry ,Spectrum Analysis ,Radical ,Analytical chemistry ,Color ,Naphthalenes ,Photochemistry ,Fluorescence ,Fluorescence spectroscopy ,Spectral line ,Cold Temperature ,Spectrometry, Fluorescence ,Ionization ,Gases ,Emission spectrum ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Laser-induced fluorescence ,Astrophysics::Galaxy Astrophysics ,Excitation - Abstract
Gas phase excitation and emission spectra of three naphthylmethyl radical chromophores are presented. These resonance-stabilized species, 1-naphthylmethyl, 2-naphthylmethyl, and α-acenaphthenyl, each possessing an sp(2) carbon adjacent to a naphthalene moiety, are studied by resonant two-color two-photon ionization, laser induced fluorescence, and dispersed fluorescence spectroscopy. Identification of the radicals is made through a combination of dispersed fluorescence and density functional theory calculations. All three species possess spectra in the 580 nm region. The possible relevance to unidentified spectroscopic features such as the diffuse interstellar bands and emission from the Red Rectangle nebula is discussed.
- Published
- 2011
36. Identification of the Jet-Cooled 1-Indanyl Radical by Electronic Spectroscopy
- Author
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Klaas Nauta, Tyler P. Troy, Raphaël G. C. R. Clady, Scott H. Kable, Nahid Chalyavi, Timothy W. Schmidt, and Masakazu Nakajima
- Subjects
Jet (fluid) ,Argon ,chemistry ,Ionization ,chemistry.chemical_element ,Photoionization ,Physical and Theoretical Chemistry ,Atomic physics ,Ionization energy ,Ground state ,Electron spectroscopy ,Fluorescence - Abstract
The electronic spectrum of the jet-cooled 1-indanyl radical has been identified in the products of a hydrocarbon discharge in argon. Electronic excitation spectra were observed in the region 20800-22600 cm(-1) by resonant two-color two-photon ionization and laser-induced fluorescence spectroscopies. In addition to the new spectrum at m/z = 117, the spectrum of 1-phenylpropargyl was also observed strongly, as was an unidentified spectrum carried by m/z = 133. The origin band of the 1-indanyl A2A''-X2A'' band system was observed at 21159 cm(-1) with the ionization potential of the radical experimentally determined to be 6.578 +/- 0.001 eV from a photoionization efficiency spectrum. Single vibronic level fluorescence was dispersed to determine the ground state vibrational frequencies that were utilized to confirm the identity of the radical in comparison with quantum chemical calculations. The calculated ground state frequencies and ionization potential, along with a calculated dispersed fluorescence spectrum of the origin band for the 1-indanyl radical, all provide a positive chemical identification.
- Published
- 2009
37. Spectroscopic Identification of the Resonance-Stabilized cis- and trans-1-Vinylpropargyl Radicals
- Author
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Timothy W. Schmidt, Kieran A Duncan, Tyler P. Troy, Scott H. Kable, Klaas Nauta, Masakazu Nakajima, Nahid Chalyavi, and Neil J. Reilly
- Subjects
Chemistry ,Radical ,General Chemistry ,Photochemistry ,Resonance (chemistry) ,Biochemistry ,Catalysis ,Fluorescence spectroscopy ,Crystallography ,Colloid and Surface Chemistry ,Unpaired electron ,Ionization ,Propargyl ,Ground state ,Cis–trans isomerism - Abstract
The cis-1-vinylpropargyl (cis-1VPR, cis-pent-4-en-1-yn-3-yl) and trans-1-vinylpropargyl (trans-1VPR, trans-pent-4-en-1-yn-3-yl) radicals, produced in a supersonically cooled hydrocarbon discharge, have been identified by a synergy of 2-dimensional fluorescence and ionization spectroscopies, revealing their electronic origin transitions at 21,232 and 21,645 cm(-1) respectively. These assignments are supported by an excellent agreement between calculated ground state frequencies of cis-1VPR and trans-1VPR with those obtained by dispersed fluorescence spectroscopy. In addition, high-resolution rotational contours of the two bands are well simulated using calculated X- and A-state trans-1VPR and cis-1VPR rotational constants. Finally, computed origin transition energies of these two isomers are within several hundred wavenumbers of the observed band positions. With the 1-phenylpropargyl radical, the 1VPR isomers are the second 1-substituted propargyl species to have been observed abundantly from a hydrocarbon discharge, while no 3-substituted analogue has been positively identified. This is likely due to the greater resonance stabilization energy of the 1-substituted species, arising from concerted delocalization of the unpaired electron over the vinyl and propargyl moieties.
- Published
- 2009
38. Unraveling the Ã1B1 ← X̃1A1 Spectrum of CCl2: The Renner−Teller Effect, Barrier to Linearity, and Vibrational Analysis Using an Effective Polyad Hamiltonian
- Author
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Klaas Nauta, Calvin Mukarakate, Haiyan Fan, Scott A. Reid, Chong Tao, Craig A. Richmond, Timothy W. Schmidt, and Scott H. Kable
- Subjects
symbols.namesake ,Renner–Teller effect ,Chemistry ,symbols ,Ab initio ,Linearity ,Isotopologue ,Rotational spectroscopy ,Physical and Theoretical Chemistry ,Atomic physics ,Hamiltonian (quantum mechanics) ,Polyad ,Excitation - Abstract
We report studies aimed at unraveling the complicated structure of the CCl 2 A (1)B 1-- X (1)A 1 system. We have remeasured the fluorescence excitation spectrum from approximately 17,500 to 24,000 cm (-1) and report the term energies and A rotational constants of many new bands for both major isotopologues (C (35)Cl 2, C (35)Cl (37)Cl). We fit the observed term energies to a polyad effective Hamiltonian model and demonstrate that a single resonance term accounts for much of the observed mixing, which begins approximately 1300 cm (-1) above the vibrationless level of the A (1)B 1 state. The derived A (1)B 1 vibrational parameters are in excellent agreement with ab initio predictions, and the mixing coefficients deduced from the polyad model fit are in close agreement with those derived from direct fits of single vibronic level (SVL) emission intensities. The approach to linearity and thus the Renner-Teller (RT) intersection is probed through the energy dependence of the A rotational constant and fluorescence lifetime measurements, which indicate a barrier height above the vibrationless level of the X (1)A 1 state of approximately 23,000-23,500 cm (-1), in excellent agreement with ab initio theory.
- Published
- 2008
39. Spectroscopic Observation of the Resonance-Stabilized 1-Phenylpropargyl Radical
- Author
-
Klaas Nauta, Scott H. Kable, Damian L. Kokkin, Timothy W. Schmidt, Neil J. Reilly, and Masakazu Nakajima
- Subjects
Free Radicals ,Molecular Structure ,Lasers ,General Chemistry ,Photochemistry ,Resonance (chemistry) ,Sensitivity and Specificity ,Biochemistry ,Fluorescence ,Catalysis ,chemistry.chemical_compound ,Spectrometry, Fluorescence ,Colloid and Surface Chemistry ,Models, Chemical ,chemistry ,Alkynes ,Ionization ,Propargyl ,Density functional theory ,Benzene ,Excitation ,Visible spectrum - Abstract
The gas-phase laser-induced fluorescence (LIF) spectrum of a 1-phenylpropargyl radical has been identified in the region 20,800-22,000 cm(-1) in a free jet. The radical was produced from discharges of hydrocarbons including benzene. Disregarding C2, C3, and CH, this radical appears as the most strongly fluorescing product in a visible wavelength two-dimensional fluorescence excitation-emission spectrum of a jet-cooled benzene discharge. The structure of the carrier was elucidated by measurement of a matching resonant two-color two-photon ionization spectrum at m/z = 115 and density functional theory. The assignment was proven conclusively by observation of the same excitation spectrum from a low-current discharge of 3-phenyl-1-propyne. The apparent great abundance of the 1-phenylpropargyl radical in discharges of benzene and, more importantly, 1-hexyne may further underpin the proposed importance of the propargyl radical in the formation of complex hydrocarbons in combustion and circumstellar environments.
- Published
- 2008
40. Structure of the Naphthalene Dimer from Rare Gas Tagging
- Author
-
Timothy W. Schmidt, Neeraj Sharma, Carine Gillieron, and Klaas Nauta
- Subjects
Resonance-enhanced multiphoton ionization ,Argon ,Chemistry ,Dimer ,chemistry.chemical_element ,Chromophore ,Mass spectrometry ,Photochemistry ,Spectral line ,chemistry.chemical_compound ,Physics::Atomic and Molecular Clusters ,Physical chemistry ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Molecular beam ,Naphthalene - Abstract
Excitation spectra of naphthalene dimer-argonn (n = 1-3) clusters are obtained by resonance enhanced multiphoton ionization time-of-flight mass spectroscopy. The spectra are generally independent of the number of attached argon atoms and reveal sharp structures which are fitted by superimposing independent monomer spectra. It is concluded that the rare-gas tagging technique reveals the presence of a T-shaped naphthalene dimer chromophore in the molecular beam.
- Published
- 2007
41. Quantum-Induced Symmetry Breaking in the Deuterated Dihydroanthracenyl Radical.
- Author
-
Krechkivska, Olha, Wilcox, Callan M., Klaas Nauta, Kable, Scott H., and Schmidt, Timothy W.
- Published
- 2019
- Full Text
- View/download PDF
42. Laser-induced fluorescence excitation and dispersed fluorescence spectroscopy of the Ã(1B1)–X̃(1A1) transition of dichlorocarbene
- Author
-
Joseph S. Guss, Scott H. Kable, Klaas Nauta, and Craig A. Richmond
- Subjects
Chemistry ,Analytical chemistry ,General Physics and Astronomy ,Fermi resonance ,Physical and Theoretical Chemistry ,Atomic physics ,Laser-induced fluorescence ,Spectroscopy ,Ground state ,Fluorescence ,Fluorescence spectroscopy ,Excitation ,Spectral line - Abstract
The A(1B1)–(1A1) transition of jet-cooled CCl2 has been investigated using both laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectroscopy. DF spectra were taken from over 90 emitting vibronic states over the breadth of the LIF spectrum. 68 ground state vibrational levels were assigned in the C35Cl2 isotopomer and 47 in C35Cl37Cl. The ground state frequencies were fit to an anharmonic potential yielding: ω″1 = 736 cm−1, ω″2 = 338 cm−1, ν″3 = 760 cm−1, x″11 = −3.19 cm−1, x″22 = −0.29 cm−1, x″12 = −1.80 cm−1, x″13 = −5.70 cm−1 and x″23 = −3.80 cm−1. This is the first gas phase measurement of ν″3. Despite the close frequency match between ν″1 and 2ν″2 there was no evidence for Fermi resonance. The intensities of transitions in the DF spectra were analysed to identify the nature of the emitting state. Levels below T00 + 2500 cm−1 in the A state could be assigned simply as combinations and overtones of ν′1 and ν′2. Between T00 + 2500 and T00 + 5300 cm−1 the emission revealed an increasing mixing between levels within the same polyad, i.e., (m,n,0), (m + 1,n − 2,0), (m + 2,n − 4,0) etc, presumably due to Fermi resonance. This mixing becomes so extensive that simple assignment of the emitting states is not possible. Above T00 + 5300 cm−1 only K′ = 0 states could be identified, indicating that the Renner–Teller intersection between the and A states had been exceeded. This intersection is therefore 22 600 cm−1 above the ground state, in excellent agreement with a previous theoretical calculation of 23 000 cm−1.
- Published
- 2005
43. Polar isomer of formic acid dimers formed in helium nanodroplets
- Author
-
Roger E. Miller, Klaas Nauta, Martina Havenith, Frank Madeja, Jana Vacek Chocholoušová, and Pavel Hobza
- Subjects
Liquid helium ,Hydrogen bond ,Formic acid ,Dimer ,Intermolecular force ,General Physics and Astronomy ,chemistry.chemical_element ,Infrared spectroscopy ,Photochemistry ,law.invention ,chemistry.chemical_compound ,Crystallography ,chemistry ,law ,Potential energy surface ,Physics::Atomic and Molecular Clusters ,Physical and Theoretical Chemistry ,Helium - Abstract
The infrared spectrum of formic acid dimers in helium nanodroplets has been observed corresponding to excitation of the "free" OH and CH stretches. The experimental results are consistent with a polar acyclic structure for the dimer. The formation of this structure in helium, as opposed to the much more stable cyclic isomer with two O-H...O hydrogen bonds, is attributed to the unique growth conditions that exist in helium droplets, at a temperature of 0.37 K. Theoretical calculations are also reported to aid in the interpretation of the experimental results. At long range the intermolecular interaction between the two monomers is dominated by the dipole-dipole interaction, which favors the formation of a polar dimer. By following the minimum-energy path, the calculations predict the formation of an acyclic dimer having one O-H...O and one C-H...O contact. This structure corresponds to a local minimum on the potential energy surface and differs significantly from the structure observed in the gas phase.
- Published
- 2004
44. Rovibronic spectroscopy of the transition in the bromochloromethylene radical
- Author
-
Klaas Nauta, Joseph S. Guss, Scott H. Kable, and Craig A. Richmond
- Subjects
Materials science ,Anharmonicity ,Observable ,Electron spectroscopy ,Fluorescence ,Molecular physics ,Atomic and Molecular Physics, and Optics ,Isotopomers ,Nuclear magnetic resonance ,Rotational spectroscopy ,Physical and Theoretical Chemistry ,Spectroscopy ,Excitation - Abstract
The A ( 1 A ′ )↔ X ( 1 A ′′ ) spectroscopy of jet-cooled CBrCl has been measured by both laser-induced fluorescence excitation and dispersed fluorescence. All three vibrational frequencies were assigned and measured in both electronic states, including the first gas phase measurements of the C–Cl stretching frequencies, ν1′′=759 and ν 1 ′ =716 cm −1 . An almost complete set of anharmonicity constants, xij, were evaluated in both electronic states. In the A state these values were measured for all isotopomers involving 35,37 Cl and 79,81 Br . The LIF spectrum was measured to the limit of observable Franck–Condon intensity. No evidence was found for shortening of the fluorescence lifetime or for large changes in the A′ rotational constant, which have been observed in other halo-carbenes and indicate the presence of other photochemical or photophysical pathways.
- Published
- 2003
45. An experimental and theoretical investigation of the triple fragmentation of CFClBr2 by photolysis near 250 nm
- Author
-
Naomi L. Haworth, George B. Bacskay, Scott H. Kable, Nathan L. Owens, and Klaas Nauta
- Subjects
Absorption spectroscopy ,Fragmentation (mass spectrometry) ,Chemistry ,Ab initio quantum chemistry methods ,Photodissociation ,Ultraviolet irradiation ,General Physics and Astronomy ,Physical chemistry ,Physical and Theoretical Chemistry ,Photochemistry ,Bond-dissociation energy ,Dissociation (chemistry) - Abstract
Photodissociation of CFClBr 2 + hν →CFCl has been shown to occur for λ 436±2 kJ mol −1 ). G3 Ab initio calculations were performed to provide estimates of Δ f H for CFClBr 2 , CFClBr, and CFCl, which were calculated to be −188±5, −43±5 and +30±5 kJ mol −1 , respectively. The dissociation energies (0 K) for sequentially breaking the C–Br bonds were calculated to be 257±5 and 183±5 kJ mol −1 , respectively. The energy required to break both C–Br bonds was calculated to be 440±5 kJ mol −1 , in excellent agreement with the experimental appearance threshold for CFCl. From the experimental appearance threshold, Δ f H (CFClBr 2 ) is estimated to be −184±5 kJ mol −1 .
- Published
- 2003
46. Rotationally resolved infrared spectroscopy of h2- and d1-formic acid monomer in liquid He droplets
- Author
-
Klaas Nauta, Frank Madeja, Phineus R. L. Markwick, Roger E. Miller, and Martina Havenith
- Subjects
Chemistry ,Liquid helium ,Overtone ,Ab initio ,Analytical chemistry ,General Physics and Astronomy ,Infrared spectroscopy ,law.invention ,law ,Ab initio quantum chemistry methods ,Physics::Atomic and Molecular Clusters ,Vibrational energy relaxation ,Density functional theory ,Fermi resonance ,Physics::Chemical Physics ,Physical and Theoretical Chemistry - Abstract
Rotationally resolved spectra of h2- and d1-formic acid embedded in liquid helium droplets have been recorded in the spectral region of the O–H (ν1) and C–H (ν2) stretch vibrations. Accidental resonant mixing between the ν1-band of h2-formic acid and the combination bands (ν2+ν7) and (ν2+ν9) has been observed. The fundamental ν1 band can interact via Fermi resonance with the (ν2+ν7), and the (ν2+ν7) via Coriolis coupling with the (ν2+ν9) band. Examination of the resonance induced line-broadening effects suggests that the helium environment modifies vibrational relaxation dynamics. The 2ν3 C=O stretch overtone is also observed and was assigned by a density functional theory (DFT) ab initio calculation. The spectroscopic constants are determined by fitting all spectra with a standard gas phase Hamiltonian.
- Published
- 2002
47. TheeΠg3 state of C2: A pathway to dissociation
- Author
-
Klaas Nauta, George B. Bacskay, B. A. Welsh, Scott H. Kable, Timothy W. Schmidt, and O. Krechkivska
- Subjects
Coupling constant ,010304 chemical physics ,Chemistry ,Ab initio ,General Physics and Astronomy ,Quantum yield ,010402 general chemistry ,01 natural sciences ,Bond-dissociation energy ,Dissociation (chemistry) ,0104 chemical sciences ,Ab initio quantum chemistry methods ,0103 physical sciences ,Molecule ,Physical and Theoretical Chemistry ,Atomic physics ,Ground state - Abstract
The lowest 13 vibrational levels, v = 0–12, of the eΠg3 state of the C2 molecule have been measured by laser-induced fluorescence of new bands of the Fox-Herzberg system. The newly observed levels, v = 5–12, which span the eΠg3 electronic state up to and beyond the first dissociation threshold of C2, were analyzed to afford highly accurate molecular constants, including band origins, and rotational and spin-orbit constants. The spin-orbit coupling constants of the previously published lowest five levels are revised in sign and magnitude, requiring an overhaul of previously published molecular constants. The analysis is supported by high level ab initio calculations. Lifetimes of all observed levels were recorded and found to be in excellent agreement with ab initio predicted values up to v = 11. v = 12 was found to exhibit a much reduced lifetime and fluorescence quantum yield, which is attributed to the onset of predissociation. This brackets the dissociation energy of ground state XΣg+1 C2 between 6.180...
- Published
- 2017
48. The energy dependence of CO(v,J) produced from H2CO via the transition state, roaming, and triple fragmentation channels
- Author
-
Klaas Nauta, Scott H. Kable, Meredith J. T. Jordan, Duncan U. Andrews, and Mitchell S. Quinn
- Subjects
Angular momentum ,010304 chemical physics ,Branching fraction ,Chemistry ,Photodissociation ,General Physics and Astronomy ,010402 general chemistry ,01 natural sciences ,Dissociation (chemistry) ,0104 chemical sciences ,Ion ,Fragmentation (mass spectrometry) ,Excited state ,0103 physical sciences ,Physical and Theoretical Chemistry ,Atomic physics ,Quantum - Abstract
The dynamics of CO production from photolysis of H2CO have been explored over a 8000 cm−1 energy range (345 nm–266 nm). Two-dimensional ion imaging, which simultaneously measures the speed and angular momentum distribution of a photofragment, was used to characterise the distribution of rotational and translational energy and to quantify the branching fraction of roaming, transition state (TS), and triple fragmentation (3F) pathways. The rotational distribution for the TS channel broadens significantly with increasing energy, while the distribution is relatively constant for the roaming channel. The branching fraction from roaming is also relatively constant at 20% of the observed CO. Above the 3F threshold, roaming decreases in favour of triple fragmentation. Combining the present data with our previous study on the H-atom branching fractions and published quantum yields for radical and molecular channels, absolute quantum yields were determined for all five dissociation channels for the entire S1←S0 abs...
- Published
- 2017
49. First observation of the 3Πg3 state of C2: Born-Oppenheimer breakdown
- Author
-
O. Krechkivska, Timothy W. Schmidt, Klaas Nauta, George B. Bacskay, Scott H. Kable, and B. A. Welsh
- Subjects
Valence (chemistry) ,010304 chemical physics ,Chemistry ,Born–Oppenheimer approximation ,Ab initio ,General Physics and Astronomy ,010402 general chemistry ,Mass spectrometry ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,Ionization ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,symbols ,Molecule ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Triplet state ,Spectroscopy - Abstract
The 33Πg state of the dicarbon molecule, C2, has been identified for the first time by a combination of resonant ionization spectroscopy, mass spectrometry, and high-level ab initio quantum chemical calculations. This marks the discovery of the final valence triplet state of C2 spectroscopically accessible from the lowest triplet state. It is found to be vibronically coupled to the recently discovered 43Πg state, necessitating vibronic calculations beyond the Born-Oppenheimer approximation to reconcile calculated rotational constants with observations. The 33Πg state of C2 is observed to have a much shorter fluorescence lifetime than expected, possibly pointing to predissociation by coupling to the unbound d3Πg state.
- Published
- 2017
50. Photodissociation of acetone from 266 to 312 nm: Dynamics of CH3 + CH3CO channels on the S0 and T1 states
- Author
-
Scott H. Kable, Kin Long Kelvin Lee, and Klaas Nauta
- Subjects
010304 chemical physics ,Internal energy ,Chemistry ,Photodissociation ,Degrees of freedom (physics and chemistry) ,General Physics and Astronomy ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Ion ,Recoil ,Ionization ,0103 physical sciences ,Available energy ,Physical and Theoretical Chemistry ,Atomic physics ,Molecular beam - Abstract
The photodissociation dynamics of acetone (CH3)2CO, cooled in a molecular beam, have been explored over the wavelength range 266–312 nm. Nascent CH3 fragments were detected by resonance-enhanced multiphoton ionization, followed by mass-selected ion imaging. For photolysis at λ = 306 nm, the image shows a sharp ring, which, when converted to a translational energy distribution, reveals a narrow Gaussian peak with a maximum at 90% of the available energy. As the photolysis energy is increased, the distribution slowly broadens and shifts to higher recoil translational energy. The fraction of available energy in translation energy decreases in favour of internal energy of the CH3CO fragment. These observations are consistent with a dynamical model in which the energy of the exit channel barrier on the T1 surface evolves mostly into relative translational energy. Energy in excess of the barrier is partitioned statistically into all degrees of freedom. No evidence was found for any other dynamical pathway produ...
- Published
- 2017
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