Search

In this work, we studied aqueous solutions of monoethanolamine (MEA), which are widely used to remove CO2 from flue and oil gases. This study combined experimental and theoretical methods of vibrational spectroscopy, using high-temperature infrared spectroscopy, quantum-chemical calculations of theoretical vibrational spectra, and structural electronic and energy characteristics of model structures. MEA has a propensity to form associations between various compositions and structures with water molecules, as well as those composed solely of water molecules. The structural and energy characteristics of such associates were analyzed in terms of their ability to interact and retain carbon dioxide. The influence of elevated temperatures and concentration of aqueous MEA solution on change in the structure of associates has also been investigated. An analysis of theoretical and experimental vibrational spectra allowed us to examine the IR spectra of MEA solutions, and identify the bands responsible for the formation of associates that would sorb CO2 well, but would delay its desorption from the solution. [ABSTRACT FROM AUTHOR]

Combined with mass spectrometry, ion spectroscopy can obtain a spectrum of the target ion by measuring its intensity change, which is induced by laser strength and wavelength. It integrates the high sensitivity of mass spectrometry and the structural specificity of spectroscopy, and thus proves to be very useful in structure characterization of complex biomolecules, such as proteins, peptides, glycans, oligonucleotides, etc. However, the electronic or vibrational spectra becomes too complex to be resolved when analyzing isomeric ions. Ion mobility spectrometry (IMS) allows ionized molecules to be separated on the basis of mobilities in the gas phase, and its coupling with electrospray and MALDI ion sources opens up possibilities for structural studies of a wide range of biomolecules in gas-phase. Ion mobility spectrometry coupled with mass spectrometry has seen spectacular growth for the last two decades. The introduction of ion mobility to ion spectroscopy has been of growing attention in recent years. While IMS can be used as an isomer filter to reduce spectral congestion of ions, highly resolved ion spectra facilitates the identification of the isomer peaks separated by IMS. Taken together, spectra and collision cross section (CCS) measurements on the same system prove to be rather useful for structural analysis and provide clearer spectroscopic fingerprint to isomers. Therefore, this paper briefly summarized advances in ion spectroscopy research based on ion mobility-mass spectrometry technology, introduced representative researches, and prospected possible development in multi-dimensional structural mass spectrometry. [ABSTRACT FROM AUTHOR]

Electronic and geometric structures of metal-free, Al, Ga and In complexes with tetrapyrazinoporphyrazine (TPyzPA) and octachlorotetrapyrazinoporphyrazine (TPyzPACl8) were investigated by density functional theory (DFT) calculations and compared in order to study the effect of chlorination on the structure and properties of these macrocycles. The nature of the bonds between metal atoms and nitrogen atoms was described using the NBO-analysis. Simulation and interpretation of electronic spectra were performed with the use of time-dependent density functional theory (TDDFT). A description of calculated IR spectra was carried out based on the analysis of the distribution of the potential energy of normal vibrational coordinates. [ABSTRACT FROM AUTHOR]

With the ever-increasing detection of sulfur-bearing molecules and the high abundance and refractory nature of aluminum, the [Al, S, O2] isomers may play an important role in the gas-phase chemistry of circumstellar envelopes and the chemistry on the surface of dust grains. High-level theoretical exploration of the [Al, S, O2] molecular system yielded five isomers, and predictions of their rotational, vibrational, and electronic spectroscopic properties are provided to inform experimental and observational searches. Cis-AlOSO and diamond isomers are isoenergetic and connected via a very small (∼1 kcal molâˆ'1) transition-state barrier. These isomers may act as intermediates along the chemical pathway between Al + SO2 and AlO + SO. Other isomers OAlOS and SAlO2 are stable relative to their corresponding dissociation asymptotes. Large permanent dipole moments of 2.521 D (cis-AlOSO), 1.239 D (diamond), and 5.401 D (OAlOS) predict strong rotational transitions and indicate these molecules as prime candidates for experimental study. Due to the low transition-state barrier, mixing of the vibrational levels is anticipated, complicating the vibrational spectrum. Electronic spectroscopy may be used as a means to differentiate between the two isomers. Strong electronic transitions are predicted to occur in the 200â€"300 nm range for cis-AlOSO and diamond. Simulated electronic absorption spectra provide a starting point for experimental characterization and spectral deconvolution of these isomers. [ABSTRACT FROM AUTHOR]

New spectroscopic parameters have been calculated to aid in the laboratory and observational detection of AlCH, AlCH+, MgCH, MgCH+, and their deuterated analogs. All species exist in linear geometry except for AlCH+, which exhibits a bent structure. Rotational frequencies have been calculated and the transition with maximum intensity is discussed for three temperature regions present in space: 100 K for a central circumstellar envelope (CSE), 30 K for an outer CSE, and 3 K indicative of the interstellar medium. Pertinent frequencies range from 25 to 250 GHz, depending on the species. At 30 K, the most intense transition is expected to be J = 4 → 3 for all species. The vibrational spectrum of each molecule is expected to be complicated due to the flat nature of the potential energy surface along the bending angle and the presence of anharmonic resonances. Deuteration produces a decrease in vibrational frequency, which may be utilized in experiments to confirm detection of these molecules. The electronic absorption spectrum of both AlCH and MgCH is predicted to be congested and broad. Various high-oscillator-strength transitions are predicted. Upon photoexcitation in the 220–300 nm region, facile dissociation on a repulsive excited state along the Al–C coordinate is predicted to be a source of Al in the colder regions of space. Photodissociation of MgCH requires several nonradiative processes that will control the product state distribution of the fragments. [ABSTRACT FROM AUTHOR]

The roadblock on the way to perform the quantum mechanical calculation as the "SCF or DFT" method for some molecules such as drugs, biological molecules, and so on is that these molecules are too large to study. They need a computer with a large amount of system memory and a very fast CPU. Therefore, we are looking for an entirely quantum-mechanical procedure to study the electronic properties of a large molecule with considerable saving computational time and acceptable accuracy. This procedure is based on searching for the active parts of a molecule, which are essentially HOMO and LUMO parts and their surroundings, and is called truncated molecule (TM) in this manuscript. To this end, at first, this procedure is inspected for Mn-complex, due to the availability of its experimental UV spectra. The calculation of the UV spectrum for TM part of Mn-complex shows λmax = 355.64 nm, while experimental UV spectra is λmax = 334.31 nm, and the corresponding theoretical value for the original molecule reveals λmax = 346.99 nm. The CPU time for the original molecule is 448,045 s that is reduced to 101,555 s for TM with acceptable accuracy (the CPU ratio is 4.41). Furthermore, this procedure is also tested for one of the sequences of A-chain of insulin, Docetaxel (drug molecule), and Taxol (drug molecule); the acceptable resemblance between UV spectra of the original and TM molecule is obtained. The computational time is reduced with a ratio of 3.59, 2.44, and 1.69, respectively. [ABSTRACT FROM AUTHOR]

Quantum chemical cluster calculations show that reactions of C+ with HCN or HNC embedded in the surface of an icy grain mantle can account for the formation of a recently detected molecule, glycolonitrile, which is considered to be an important precursor to ribonucleic compounds. Reactions of cations deposited on ice mantles with minimal kinetic energy have been found theoretically to result in previously unknown pathways to significant organic compounds in protostellar systems and the interstellar medium. In density functional theory cluster calculations involving up to 24H2O, C+ reacts consistently with HCN embedded in ice to yield the neutral HOCHNC radical with no barrier, along with H3O+ as a byproduct. If HOCHNC then reacts with H, three species can be formed: HOCH2NC (isocyanomethanol), HOCH2CN (glycolonitrile), and HOCHNCH. For the C++ HNC reaction on ice, the HOCHCN and H2OCCN radicals form as intermediates, the first of which is another direct precursor to glycolonitrile via H addition. In addition to characterizing reaction pathways, predictions are provided of the vibrational and electronic spectra of the HCN and HNC starting clusters and the HOCHNC ice-bound intermediate. [ABSTRACT FROM AUTHOR]

A generalization of the Raman scattering (RS) spectrum, the Raman excitation map (REM) is a hyperspectral two-dimensional (2D) data set encoding vibrational spectra, electronic spectra and their coupling. Despite the great potential of REM for optical sensing and characterization with remarkable sensitivity and selectivity, the difficulty of obtaining maps and the length of time required to acquire them has been practically limiting. Here we show, with a simple setup using current optical equipment, that maps can be obtained much more rapidly than before (~ms to ~100 s now vs. ~1000 s to hours before) over a broad excitation range (here ~100 nm is demonstrated, with larger ranges straightforward to obtain), thus taking better advantage of scattering resonance. We obtain maps from different forms of carbon: graphite, graphene, purified single walled carbon nanotubes (SWCNTs) and chirality enriched SWCNTs. The relative speed and simplicity of the technique make REM a practical and sensitive tool for chemical analysis and materials characterization. [ABSTRACT FROM AUTHOR]

Gas phase emission spectra of the hitherto unknown free radical LiSb were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which antimony vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. A number of blue-degraded bands observed in the range 6200–7800 cm −1 are assigned to transitions from four excited states A 2 1, A 3 0 + , A 4 0 − and a 2 to the X 1 0 + and/or X 2 1 components of the X 3 Σ − ground state. The 0–0 bands of six transitions were measured at high spectral resolution and rotationally analysed. The rotational and vibrational analyses have yielded the spectroscopic parameters of all six states. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential energy curves and spectroscopic constants for the low-lying states of LiSb as well as electric-dipole transition moments and radiative lifetimes. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2-Hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) were investigated through MD simulations and DFT calculations. • Properties derived from simulations were compared to experimental electronic and vibrational spectra. • Different solvation models were used in theoretical spectra calculation. 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) are monomers widely used in the production of hydrogels with medium-high water content. The structural and spectroscopic properties of HEMA and AA were studied using a combination of computational strategies based on both density functional theory (DFT) calculations and molecular dynamics (MD) simulations. DFT calculations have confirmed the co-existence of two stable HEMA conformers, while solute-solvent interactions between HEMA and AA with water were characterized by the analysis of MD simulations carried out by employing four different water models and different simulation conditions. The carbonyl and hydroxyl oxygen atoms of HEMA are involved in hydrogen bonding, whereas the ester oxygen atom does not appreciably interacts with the solvent. No significant differences in solute-solvent interactions are found between the two HEMA conformers. Their spectroscopic properties were calculated and the results were compared to experimental data. Although electronic spectra do not really allow a differentiation of the conformers, IR spectra present some peculiar bands to discriminate the presence and obtain information on the ratio of the conformers in solution. To verify the influence of a solvent with higher dipole moment on chemical properties, acetonitrile has been considered as an alternative solvent. [ABSTRACT FROM AUTHOR]

[Display omitted] • The rotationally resolved absorption spectrum of A ∼ 2Σ+– X ∼ 2Π 3/2 for ICN+ was observed. • The rotational constants of both the electronic states were precisely determined. • The rotational constants of FCN+, ClCN+, and BrCN+ were theoretically evaluated. • The rotational profiles of ClCN+ were simulated to identify this cation in space. A rotationally resolved gas-phase absorption spectrum of the A ∼ 2Σ+– X ∼ 2Π 3/2 electronic transition of the cyanogen iodide radical cation ICN+ was observed by cavity ring-down spectroscopy for the first time. This cation was produced in a supersonic planar discharge jet through a mixture of ICN in helium. By the aid of a program for rotational, vibrational and electronic spectra PGOPHER, the rotational constants were determined to be 0.10700(12) and 0.11002(12) cm−1 for the A ∼ 2Σ+ and X ∼ 2Π 3/2 electronic states, respectively, and the band origin to be 18262.083(3) cm−1. The rotational constant ratio β {= (B ′− B ″)/ B ″} was determined to be −2.8%. The β values for FCN+, ClCN+, BrCN+, and ICN+ were also evaluated theoretically by CAM-B3LYP/CEP-121G using Gaussian 09W. The rotational profile of the absorption band and its temperature dependence for ClCN+, one of the important candidates for Diffuse Interstellar Bands, were simulated, aiding us in the identification of this cation as in interstellar space. [ABSTRACT FROM AUTHOR]

A detailed mechanistic investigationof the early stages of thePaternò–Büchi reaction following 267 nm excitationof benzaldehyde in cyclohexene has been completed using ultrafast,broadband transient UV–visible and IR absorption spectroscopies.Absorption due to electronically excited triplet state benzaldehydedecays on a 80 ps time scale via reaction with cyclohexene. The growthand subsequent decay of the biradical intermediate produced followingC–O bond formation is followed by transient vibrational spectroscopy.The biradical decays by ring closure to an oxetane or by dissociating,reforming the ground state reactants. Detailed kinetic analysis allowedderivation of quantum yields and rate constants for these competingbiradical decay processes, ϕoxetane= 0.53, ϕdiss= 0.47, koxetane= 0.27 ±0.09 ns–1and kdiss=0.24 ± 0.09 ns–1. This study provides a strikingillustration of the ways in which contemporary ultrafast transientabsorption spectroscopy methods can be used to dissect the mechanismand kinetics of a classic photoreaction. [ABSTRACT FROM AUTHOR]

• The non-fluorescence of the FLVN-OCN is ascribed to obvious charge transfer. • The fluorescence enhancement of the HPO is the result of ESIPT mechanism. • The electronic spectra measured experimentally is ascribed to the HPO-PT. • The PECs indicate that the proton transfer process of HPO occurs in the S 1 state. The photophysical and photochemical properties of the novel sensor 3-(cyanooxy)-hydroxyflavone (FLVN-OCN) and 3-hydroxyflavone (HPO) generated by the reaction with hydrogen sulfide (H 2 S) have been investigated theoretically. Analysis of structure parameters and infrared vibrational spectra indicate that hydrogen bond is strengthened in the first (S 1) excited state, which is beneficial to the excited-state intramolecular proton transfer (ESIPT). The strength of hydrogen bond is determined by the reduced density gradient model. The calculated absorption and emission spectra of the tautomer (HPO-PT) are located at 412.5 and 536.8 nm, respectively, which are in good agreement with the experimental values (425 and 525 nm). The results show that the measured spectra experimentally are ascribed to HPO-PT configuration. Combined with the frontier molecular orbital and hole-electron analysis, the electron density of the product HPO transfers from the oxygen atom on the hydroxyl group to the adjacent oxygen atom, which affects the fluorescence properties, resulting in significant fluorescent changes with the addition of H 2 S. The obtained energy barrier of the S 1 state (4.22 kcal/mol) is lower than that of the ground (S 0) state (14.58 kcal/mol) through the potential energy curves (PECs) of HPO, which further indicates that the ESIPT process is more likely to occur in the S 1 state. The work explains the detection mechanism for H 2 S of the fluorescent probe FLVN-OCN and provides a reference for the further study of this probe. [ABSTRACT FROM AUTHOR]

The Knudsen effusion method with mass spectrometric control of the vapor composition was used to study the possibility of a congruent transition to the gas phase and to estimate the enthalpy of sublimation of metal-free tetrakis(1,2,5-thiadiazolo)porphyrazine and its nickel complex (H2TTDPz and NiTTDPz, respectively). The geometrical and electronic structure of H2TTDPz and NiTTDPz in ground and low-lying excited electronic states were determined by DFT calculations. The electronic structure of NiTTDPz was studied by the complete active space (CASSCF) method, following accounting dynamic correlation by multiconfigurational quasi-degenerate second-order perturbation theory (MCQDPT2). A geometrical structure of D2h and D4h symmetry was obtained for H2TTDPz and NiTTDPz, respectively. According to data obtained by the MCQDPT2 method, the nickel complex possesses the ground state 1A1g, and the wave function of the ground state has the form of a single determinant. Electronic absorption and vibrational (IR and resonance Raman) spectra of H2TTDPz and NiTTDPz were studied experimentally and simulated theoretically. [ABSTRACT FROM AUTHOR]

• HOMO-LUMO energy gaps of compounds with the π-extended conjugation are significantly decreased, leading to the red-shift of electronic spectra. • Compounds with the π-extended conjugation (M3HN , M2HQC , and M3HQC) have remarkably large Stokes shifts of about 1000 cm−1. • ESIPT reactions of studied compounds are observed in an ultrafast timescale with the remarkably high PT probability. Effects of nitrogen substitution and π-conjugation on the strength of intramolecular hydrogen bond (H-bond), photophysical properties, and excited-state intramolecular proton transfer (ESIPT) reactions of MS derivatives have been systematically investigated using DFT and TD-DFT methods at the B3LYP/TZVP level. The H-bond strength of all studied compounds becomes stronger in the S 1 than in the S 0. This result is confirmed by vibrational IR spectra and topological analysis. The H-bond strength of nitrogen substituted compounds is lower than those of compounds with the π-extended conjugation. For photophysical properties, the HOMO-LUMO energy gaps in normal and tautomer forms of nitrogen substituted compounds are insignificantly increased, whereas those of compounds with the π-extended conjugation are notably decreased. The slight widening of the energy gaps results in the slight blue-shifts of the absorption and emission peaks of nitrogen substituted compounds compared to those of MS , whereas the significant narrowing of the energy gaps makes the incredible red-shifts of both electronic spectra of compounds with the π-extended conjugation. Thus, remarkably large Stokes shifts of about 1000 cm−1 are observed for compounds with the π-extended conjugation (M3HN , M2HQC , and M3HQC). In addition, potential energy curves along the PT reaction indicate that the ESIPT of all studied compounds should occurred due to low PT barriers in the exothermic reaction. Dynamic simulations reveal that the ESIPT reactions of studied compounds are observed in an ultrafast time scale (38–130 fs). Most of them have remarkably high PT probabilities (0.84–1.00) except M3HP (0.56), which are in good agreement with the results of H-bond strength. Therefore, the photophysical properties of studied compounds can be significantly tuned by controlling the effect of π-conjugation. [ABSTRACT FROM AUTHOR]