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Doping the hydrogen-disordered phases of ice V, VI, and XII with hydrochloric acid (HCl) has led to the discovery of their hydrogen-ordered counterpart ices XIII, XV, and XIV. Yet, the mechanistic details of the hydrogen-ordering phase transitions are still not fully understood. This includes, in particular, the role of the acid dopant and the defect dynamics that it creates within the ices. Here we investigate the effects of a wide range of acid and base dopants on the hydrogen ordering of ices V and VI with calorimetry and X-ray diffraction. Surprisingly, lithium-hydroxide doping achieves a performance comparable to hydrofluoric-acid doping in ice V, but it is ineffective in the case of ice VI. Ice V is therefore the first phase of ice that can be hydrogen-ordered with both acid and base doping. Hydrobromic-acid doping facilitates hydrogen ordering of ice VI, but it is ineffective in the case of ice V. HCl is reaffirmed to be the most effective for both phases which is attributed to a favorable combination of high solubility and strong acid properties. Sodium-hydroxide, potassium-hydroxide (as previously shown), and perchloric-acid doping are ineffective for both phases. These findings highlight the need for future computational studies but also raise the question why lithium hydroxide is the best-performing alkali hydroxide for hydrogen-ordering ice V whereas potassium-hydroxide doping is most effective for the “ordinary” ice Ih. [ABSTRACT FROM AUTHOR]

2,4,6-trichloroanisole and 2,4,6-tribromoanisole were investigated by means of electron transmission spectroscopy and two different types of dissociative electron attachment spectrometers. The results obtained were interpreted with the support of density functional theory calculations. The dominant dissociative decay channels of the temporary molecular negative ions lead to the formation of Cl- and Br-in the low electron energy region. Formation of long-lived parent anions is observed at thermal electron energies. Their relative intensity depends on the experimental time window, ∼36 μs in the case of the static magnet mass analyzer and ∼200 μs for the quadrupole mass analyzer employed. The results obtained may be useful for rapid detection of these compounds in wine and pharmaceutical industries, as well as other branches connected to the food industry, e.g., packaging. [ABSTRACT FROM AUTHOR]

Three spin-orbit states, 1²Π1/2, 2²Π3/2, and 2²Π1/2, of chloroiodine anion (ICl-) formed by lowenergy electron attachment in the Franck-Condon region are associated with the dissociative limits of I- (¹S0) and Cl (²P3/2) or Cl* (²P1/2) fragments. Within the adiabatic scheme, the presumptive Π-symmetry of the fragment angular distributions is dramatically changed to be the Π-Σ mixing symmetry, due to the significant spin-orbit interaction effect on the electronic state couplings of ICl-. The present experimental approach also enables us to separate the contributions of different electronic states from the mixed states, providing a crucial method for quantitatively evaluating the configuration-interaction wavefunctions. [ABSTRACT FROM AUTHOR]

We report a detailed study on the IR spectroscopy of HCl-water complexes in superfluid helium nanodroplets in the frequency range from 2660 to 2675 cm-1. We have recorded spectra of HCl-H216O as well as of HCl-H218O complexes and compared these results with theoretical predictions. In addition, we have carried out mass-selective intensity measurements as a function of partial pressure of HCl as well as of H218O (pick-up curves). The results support a scenario where the IR-absorption in this part of the spectrum contains contributions from undissociated as well as from dissociated clusters with Cl-(H2O)3(H3O)+ being the smallest dissociated complex. These findings are corroborated by additional electric field measurements yielding the orientation of the vibrational transition moment with respect to the permanent dipole moment. As a result we are able to assign a broad absorption band starting at 2675 cm-1 to dissociated HCl-water clusters (HCl)1(H2O)n with n >= 4. The two narrow absorption lines at 2667.9 cm-1 and 2670 cm-1 are assigned to an undissociated cluster, in agreement with previous studies. [ABSTRACT FROM AUTHOR]

After almost two decades of high resolution molecular spectroscopy in superfluid helium droplets, the understanding of microsolvation is still the subject of intense experimental and theoretical research. According to the published spectroscopic work including microwave, infrared, and electronic spectroscopy, the latter appears to be particularly promising to study microsolvation because of the appearance of pure molecular transitions and spectrally separated phonon wings. Instead of studying the very details of the influence of the helium environment for one particular dopant molecule as previously done for phthalocyanine, the present study compares electronic spectra of a series of non-polar porphyrin derivatives when doped into helium droplets consisting of 104-105 helium atoms. Thereby, we focus on the helium-induced fine structure, as revealed most clearly at the corresponding electronic origin. The interpretation and the assignment of particular features obtained in the fluorescence excitation spectra are based on additional investigations of dispersed emission spectra and of the saturation behavior. Besides many dopant-specific results, the experimental study provides strong evidence for a particular triple peak feature representing the characteristic signature of helium solvation for all seven related dopant species. [ABSTRACT FROM AUTHOR]

Electronegativity is a well-known property of atoms and substituent groups. Because there is no direct way to measure it, establishing a useful scale for electronegativity often entails correlating it to another chemical parameter; a wide variety of methods have been proposed over the past 80 years to do just that. This work reports a new approach that connects electronegativity to a spectroscopic parameter derived from resonant inelastic x-ray scattering. The new method is demonstrated using a series of chlorine-containing compounds, focusing on the Cl 2p-1LUMO1 electronic states reached after Cl 1s → LUMO core excitation and subsequent KL radiative decay. Based on an electron-density analysis of the LUMOs, the relative weights of the Cl 2pz atomic orbital contributing to the Cl 2p3/2 molecular spin-orbit components are shown to yield a linear electronegativity scale consistent with previous approaches. [ABSTRACT FROM AUTHOR]

Hydrogen- and lithium-bonded complexes of A-H/Li (A = F, Cl) with the amine analogues NF3, NH3, and NH2(CH3) were studied at the MP2/6-311++G(d,p) level of theory. Bond extensions and redshifts were obtained for the H-bonded complexes, while bond extensions and blueshifts were obtained for the Li-bonded species. The variation of these and other properties with the basicity of the amines was investigated and rationalized by comparing the ab initio results with predictions from a model derived from perturbation theory. [ABSTRACT FROM AUTHOR]

Based on a multiple scale analysis of a forced reaction-diffusion system leading to amplitude equations, we explain the existence of spiral wave and its photo-induced spatiotemporal behavior in chlorine dioxide-iodine-malonic acid system. When the photo-illumination intensity is modulated, breathing of spiral is observed in which the period of breathing is identical to the period of forcing. We have also derived the condition for breakup and suppression of spiral wave by periodic illumination. The numerical simulations agree well with our analytical treatment. [ABSTRACT FROM AUTHOR]

We present a systematic investigation of the accuracy of the various theories and basis sets that can be applied to study the interaction of Cl- ions with Ar atoms. It is conclusively shown that gaseous ion mobility can distinguish among theoretical ion-neutral interaction potentials. Based on the conclusions, high-level ab initio potential energy curves are obtained for all of the Cl--RG (RG = He-Rn) complexes. Spectroscopic constants have been derived from these potentials and are compared to a range of theoretical and experimental data, to which they generally show good agreement. General trends are discussed in comparison to other halogen-rare gas complexes previously studied. The potentials also have been tested by using them to calculate transport coefficients for Cl- moving through a bath of RG atoms. [ABSTRACT FROM AUTHOR]

The photochemistry of Cl2O (dichlorine monoxide) was studied using measurements of its UV/vis absorption spectrum temperature dependence and the O(3P) atom quantum yield, [uppercase_phi_synonym]Cl2OO(λ), in its photolysis at 193 and 248 nm. The Cl2O UV/vis absorption spectrum was measured over the temperature range 201-296 K between 200 and 500 nm using diode array spectroscopy. Cl2O absorption cross sections, σCl2O(λ,T), at temperatures <296 K were determined relative to its well established room temperature values. A wavelength and temperature dependent parameterization of the Cl2O spectrum using the sum of six Gaussian functions, which empirically represent transitions from the ground 1A1 electronic state to excited states, is presented. The Gaussian functions are found to correlate well with published theoretically calculated vertical excitation energies. O(3P) quantum yields in the photolysis of Cl2O at 193 and 248 nm were measured using pulsed laser photolysis combined with atomic resonance fluorescence detection of O(3P) atoms. O(3P) quantum yields were measured to be 0.85 ± 0.15 for 193 nm photolysis at 296 K and 0.20 ± 0.03 at 248 nm, which was also found to be independent of temperature (220-352 K) and pressure (17 and 28 Torr, N2). The quoted uncertainties are at the 2σ (95% confidence) level and include estimated systematic errors. ClO radical temporal profiles obtained following the photolysis of Cl2O at 248 nm, as reported previously in Feierabend et al. [J. Phys. Chem. A 114, 12052, (2010)], were interpreted to establish a <5% upper-limit for the O + Cl2 photodissociation channel, which indicates that O(3P) is primarily formed in the three-body, O + 2Cl, photodissociation channel at 248 nm. The analysis also indirectly provided a Cl atom quantum yield of 1.2 ± 0.1 at 248 nm. The results from this work are compared with previous studies where possible. [ABSTRACT FROM AUTHOR]

Following up our preliminary communication [Kawamata et al., Phys. Chem. Chem. Phys. 10, 4378 (2008)], the effects of the antisymmetric-stretching excitation of methane on the Cl(2P3/2)+CH4 reaction are examined here over a wide range of initial collision energy in a crossed molecular beam imaging experiment. The antisymmetric stretch of CH4 is prepared in a single rovibrational state of (v3=1, j=2) by direct infrared absorption, and the major product states of CH3(v=0) are probed by a time-sliced velocity-map imaging method. We find that at fixed collision energies, the stretching excitation promotes reaction rate. Compared to the ground-state reaction, this vibrational enhancement factor is, however, no more effective than the translational enhancement. The correlated HCl(v′=1) vibrational branching fraction shows a striking dependence on collision energies, varying from 0.7 at Ec=2 kcal mol-1 to about 0.2 at 13 kcal mol-1. This behavior resembles the previously studied Cl+CH2D2(v6=1), but is in sharp contrast to the Cl+CHD3(v1=1) and CH2D2(v1=1) reactions. Dependences of experimental results on the probed rotational states of CH3(v=0) are also elucidated. We qualitatively interpret those experimental observations based on a conceptual framework proposed recently. [ABSTRACT FROM AUTHOR]

Following up our preliminary communication [Kawamata et al., Phys. Chem. Chem. Phys. 10, 4378 (2008)], the effects of the antisymmetric-stretching excitation of methane on the Cl(2P3/2)+CH4 reaction are examined here over a wide range of initial collision energy in a crossed molecular beam imaging experiment. The antisymmetric stretch of CH4 is prepared in a single rovibrational state of (v3=1, j=2) by direct infrared absorption, and the major product states of CH3(v=0) are probed by a time-sliced velocity-map imaging method. We find that at fixed collision energies, the stretching excitation promotes reaction rate. Compared to the ground-state reaction, this vibrational enhancement factor is, however, no more effective than the translational enhancement. The correlated HCl(v′=1) vibrational branching fraction shows a striking dependence on collision energies, varying from 0.7 at Ec=2 kcal mol-1 to about 0.2 at 13 kcal mol-1. This behavior resembles the previously studied Cl+CH2D2(v6=1), but is in sharp contrast to the Cl+CHD3(v1=1) and CH2D2(v1=1) reactions. Dependences of experimental results on the probed rotational states of CH3(v=0) are also elucidated. We qualitatively interpret those experimental observations based on a conceptual framework proposed recently. [ABSTRACT FROM AUTHOR]

We report a study of chlorine atom reactions with a series of target monounsaturated alkene molecules: 1-pentene, 1-hexene, 2-hexene, and cyclohexene. These reactions were studied using crossed-beam dc slice ion imaging at collision energies of 4 and 7 kcal/mol. Images of the reactively scattered alkenyl radical products were obtained via single photon ionization at 157 nm. The angular distributions at low collision energy are largely isotropic, suggesting the formation of a complex that has a lifetime comparable to or longer than its rotational period, followed by HCl elimination. At high collision energy, the distributions show a sharp forward peak superimposed on the isotropic component accounting for ∼13% of the product flux. The translational energy distributions peak near zero for the backscattered product, in sharp contrast to the results for alkanes. In the forward direction, the translational energy distributions change dramatically with collision energy. At the high collision energy, a sharp forward peak at ∼80% of the collision energy appears, quite reminiscent of results of our recent study of Cl+pentane reactions. The scattering distributions for all target molecules are similar, suggesting similarity of the reaction dynamics among these molecules. Ab initio calculations of the energetics and ionization energies for the various product channels were performed at the CBS-QB3 level to aid in interpreting the results. [ABSTRACT FROM AUTHOR]

Electron attachment to chlorine azide (ClN3) was studied using a flowing-afterglow Langmuir-probe apparatus. Electron attachment rates were measured to be 3.5×10-8 and 4.5×10-8 cm3 s-1 at 298 and 400 K, respectively, with an estimated 35% absolute accuracy. Cl- was the sole ion product of the attachment reaction; weak ion signals were observed for other anions and attributed to impurities and secondary ion-molecule reactions. Assuming a relative uncertainty of ±10% for these data, an activation energy for the attachment reaction may be given as 24±10 meV. [ABSTRACT FROM AUTHOR]

Solvated ions are a fundamental constituent of many biological systems. An important class consists of the alkali cations. In particular, potassium (K+) is the most abundant ion in the cytoplasm, whereas lithium (Li+), rubidium (Rb+), and cesium (Cs+) are of fundamental physicochemical and medical relevance. A powerful tool to understand ion specificity and cellular systems on a microscopic level is provided by molecular dynamics simulations. Previously, reliable force field parameters for Li+, K+, Rb+, and Cs+ in aqueous solution have not been available for the simple point charge (SPC) water model widely used in conjunction with the GROMOS force field. We used the Kirkwood–Buff theory to develop force fields for Li+, K+, Rb+, and Cs+ in SPC water to reproduce experimental data on respective aqueous alkali chloride solutions (LiCl, KCl, RbCl, CsCl). The force field developed reproduces many of the known properties of alkali metal chlorides solutions including densities and partial molar volumes. Our force field is shown to be superior to other common alkali chloride force fields in terms of reproducing the activity derivative, as a prerequisite for a realistic measure of ion-solute association underlying ion-specific phenomena (Hofmeister effects). For lithium and potassium, the ionic radii from cation-water oxygen pair correlation functions and hydration numbers are well reproduced. The force field developed will be useful for modeling physiological conditions and ion-specific phenomena for biomolecular systems. [ABSTRACT FROM AUTHOR]

Velocity imaging technique combined with (2+1) resonance-enhanced multiphoton ionization (REMPI) is used to detect primary photodissociation of propionyl chloride. In one-color experiments at 235 nm, the Cl and Cl* fragments are produced rapidly, leading to a fraction of translational energy release of 0.37 and 0.35, anisotropy parameters of 1.1 and 0.8, and quantum yield of 0.67 and 0.33, respectively, when initial excitation of the 1(n, π*)CO band is coupled to the 1(nCl, σC–Cl*) repulsive configuration. The resulting propionyl radical with sufficient internal energy may undergo secondary dissociation to yield CO that is characteristic of an isotropic distribution. The REMPI spectra of the CO (0,0) and (1,1) bands are measured, giving rise to a Boltzmann rotational temperature of 1200 and 770 K, respectively, and a Boltzmann vibrational temperature of 2800 K. A minor channel of HCl elimination is not detected, probably because of predissociation in two-photon absorption at 235 nm. In two-color experiments comprising an additional 248 nm photolyzing laser, Cl and Cl* are produced with a fraction of translational energy release of 0.43 and 0.40 and anisotropy parameters of 1.0 and 0.6, respectively. The secondary production of CO is not observed although the internal energy partitioned in the propionyl radical is in the proximity of the dissociation barrier. In either experimental scheme, a small component appearing in the center of the Cl and Cl* images is proposed to stem from ground state dissociation via internal conversion. [ABSTRACT FROM AUTHOR]

In this study we present the results of a first principles molecular dynamics simulation of a single 1-ethyl-3-methyl-imidazolium chloride [C2C1im][Cl] ion pair dissolved in 60 water molecules. We observe a preference of the in plane chloride coordination with respect to the cation ring plane as compared to the energetic slightly more demanding on top coordination. Evaluation of the different radial distribution functions demonstrates that the structure of the hydration shell around the ion pair differs significantly from bulk water and that no true ion pair dissociation in terms of completely autonomous solvation shells takes place on the timescale of the simulation. In addition, dipole moment distributions of the solvent in distinct solvation shells around different functional parts of the [C2C1im][Cl] ion pair are calculated from maximally localized Wannier functions. The analysis of these distributions gives evidence for a depolarization of water molecules close to the hydrophobic parts of the cation as well as close to the anion. Examination of the angular distribution of different OH(H2O)–X angles in turn shows a linear coordination of chloride accompanied by a tangential orientation of water molecules around the hydrophobic groups, being a typical feature of hydrophobic hydration. Based on these orientational aspects, a structural model for the obvious preference of ion pair association is developed, which justifies the associating behavior of solvated [C2C1im][Cl] ions in terms of an energetically favorable interface between the solvation shells of the anion and the hydrophobic parts of the cation. [ABSTRACT FROM AUTHOR]

Midinfrared spectra of HCl dimers have been obtained in helium nanodroplets. The interchange-tunneling (IT) splitting in the vibrationally excited state of the bonded H–Cl stretching band (ν2) in (H35Cl–H37Cl) dimers was measured to be 2.7±0.2 cm-1, as compared to 3.7 cm-1 in free dimer. From the splitting, the strength of the IT coupling in liquid helium of 0.85±0.15 cm-1 was obtained, which is about a factor of 2 smaller than in the free dimer. The results are compared with the previous spectroscopic study of (HF)2 in He droplets as well as the theoretical study of (HF)2 and (HCl)2 dimers in small He clusters. [ABSTRACT FROM AUTHOR]

Thermal electron attachment to SF5Cl has been studied with the flowing afterglow Langmuir probe technique. The rate coefficient is moderate, 4.8(±1.2)×10-8 cm3 s-1, and invariant with temperature over the temperature range of 300–550 K. The reaction is dissociative, forming mainly SF5-+Cl. Minor yields of Cl- and FCl- were also found. The yields of the minor channels increase slightly with temperature. Statistical unimolecular rate modeling is employed to elucidate the character of the dissociation pathways and to support the assumption that the dissociations involve the formation of metastable anionic SF5Cl-. [ABSTRACT FROM AUTHOR]

Computations of structures and total energies have been carried out for neutral and anionic SFnCl (n=0–5), using the composite G3 method and density functional theory (DFT) at the B3LYP/6-311+G(3df) level. The total energies and zero-point energies have been used here to derive electron affinities, bond dissociation energies, and heats of formation. In addition, vibrational frequencies, polarizabilities, and dipole moments are reported. Results are compared with earlier work for SFm (m=1–6) and demonstrate how the relatively weak S–Cl bond and reduced symmetry influence the properties of these molecules and anions. Comparisons are also made between G3 and DFT results for SFnCl. Of particular interest is the alternating pattern of agreement between calculated electron affinity values with n. These calculations also provide critical energetic data needed to understand experimental measurements of electron attachment to SF5Cl [Van Doren et al., J. Chem. Phys. 128, 094309 (2008)] for which numerous ion products have been reported in the literature at low electron energy. [ABSTRACT FROM AUTHOR]

The photoelectron spectra of the ClH2- and ClD2- anions have been simulated using a Franck–Condon model involving vertical excitation to the four coupled quasidiabatic potential energy surfaces that correlate with Cl(2P)+H2(1Σg+). A careful analysis of the excitation process is presented. All electrostatic, spin-orbit, and Coriolis couplings in the photodetached ClH2 (ClD2) neutral are included. At a resolution of 1 meV, the resulting spectra are dominated by the bound and resonant states of the Cl...H2 and Cl...D2 van der Waals complexes, along with contributions from the associated continua. Only small differences occur between these spectra and those simulated under the assumption that each of the three electronically adiabatic Cl(2P)+H2 states can be treated separately. In particular, photodetachment to form the Cl*(2P1/2)H2 complex leads to very low intensity of spectral features associated with Cl(2P3/2)H2. This clearly implies that, while nonadiabatic effects do have some influence on the bound and resonance state energies of both complexes as shown recently by Garand et al. [Science 319, 72 (2008)], nonadiabatic transitions between the two complexes are extremely rare. [ABSTRACT FROM AUTHOR]

The photoelectron spectra of the ClH2- and ClD2- anions have been simulated using a Franck–Condon model involving vertical excitation to the four coupled quasidiabatic potential energy surfaces that correlate with Cl(2P)+H2(1Σg+). A careful analysis of the excitation process is presented. All electrostatic, spin-orbit, and Coriolis couplings in the photodetached ClH2 (ClD2) neutral are included. At a resolution of 1 meV, the resulting spectra are dominated by the bound and resonant states of the Cl...H2 and Cl...D2 van der Waals complexes, along with contributions from the associated continua. Only small differences occur between these spectra and those simulated under the assumption that each of the three electronically adiabatic Cl(2P)+H2 states can be treated separately. In particular, photodetachment to form the Cl*(2P1/2)H2 complex leads to very low intensity of spectral features associated with Cl(2P3/2)H2. This clearly implies that, while nonadiabatic effects do have some influence on the bound and resonance state energies of both complexes as shown recently by Garand et al. [Science 319, 72 (2008)], nonadiabatic transitions between the two complexes are extremely rare. [ABSTRACT FROM AUTHOR]

The collision-induced reaction of Xe+ with HCl has been studied by use of classical dynamics procedures at collision energies 2–20 eV using empirical potential parameters. The principal reaction pathway on the potential energy surface is the formation of XeH+ with the maximum reaction cross section, 1.2 Å2, occurring at E=9 eV. At lower energies, the cross section for the charge transfer process Xe++HCl→Xe+HCl+ is comparable to that for XeH+ formation, but at higher energies, it is larger by a factor of 2. The cross section of the XeCl+ formation is an order of magnitude smaller than that of XeH+. For both XeH+ and XeCl+ formations, the reaction threshold is ≈2 eV. The XeH+ formation takes place immediately following the turning point in a direct-mode mechanism, whereas an indirect-mode mechanism operates in the formation of XeCl+. Both XeH+ and XeCl+ formations come mainly from the perpendicular configuration, Xe+...HCl, at the turning point. Product vibrational excitation is found to be strong in both XeH+ and XeCl+. [ABSTRACT FROM AUTHOR]

The first singlet-singlet electronic system, S1←S0, in thiophosgene has been recorded as a laser induced fluorescence (LIF) excitation and an optical-optical double resonance (OODR) spectrum under jet-cooled conditions. In the OODR process, the sum of the frequencies of the pump and probe lasers must be fixed to the energy difference between a pair of vibronic levels in the S2(v′) and S0(v″) states. Detection is through the fluorescence from the S2 state. The blocking of a spectrum into its four possible symmetry components is obtained by adjusting the total pump+probe energy such that it matches the energy difference between symmetry selected levels in the S2 and S0 electronic states. In this method the pump laser is used to excite a group of “hot” sequence bands that involve combinations of the ν4 and ν6 antisymmetric vibrations. The additional data that were collected by this method were used to update and refine the analyses of the spectrum. Magnetic dipole transitions are reported for the first time. [ABSTRACT FROM AUTHOR]

The state-selective positive-ion and negative-ion dissociation pathways of gaseous and condensed Si(CH3)2Cl2 following Cl 2p, Cl 1s, and Si 2p core-level excitations have been characterized. The excitations to a specific antibonding state (15a1* state) of gaseous Si(CH3)2Cl2 at the Cl 2p, Cl 1s, and Si 2p edges produce significant enhancement of fragment ions. This ion enhancement at specific core-excited states correlates closely with the ion kinetic energy distribution. The results deduced from ion kinetic energy distribution are consistent with results of quantum-chemical calculations on Si(CH3)2Cl2 using the ADF package. The Cl- desorption yields for Si(CH3)2Cl2/Si(100) at ∼90 K are notably enhanced at the 15a1* resonance at both Cl 2p and Si 2p edges. The resonant enhancement of Cl- yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide insight into the state-selective ionic fragmentation of molecules via core-level excitation. [ABSTRACT FROM AUTHOR]

Accurate thermochemical data of small molecules are invaluable to the progress of every aspect of chemistry, especially in the atmosphere, combustion and industry. In this work, photofragmentation translational spectroscopy and 1st principles electronic structure theory reveal the literature value of the heat of formation of chlorine-isocyanate to be in error by more than 40 kcal/mol. We report a revised experimental value for D0(Cl–NCO)=51±3 kcal/mol which leads to a ΔHf (ClNCO)=8.5±3 kcal/mol. High level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit give D0(Cl–NCO)=56.3 kcal/mol, in good agreement with experiment. In light of the present results, the destabilization of azides relative to isoelectronic isocyanates has been evaluated empirically for three pairs of related molecules. It is found to be 90–110 kcal/mol, and has been attributed mainly to the weakening of the N–NN bond relative to the N–CO bond. Electronic structure calculations employing decomposition analysis suggest that, compared to homopolar N2, the +δCO-δ π polarity provides better orbital interaction (charge transfer) and electrostatic attraction and results in a closer encounter and larger stabilization between the fragments and that this is the origin of isoelectronic destabilization of azides relative to the isocyanates. [ABSTRACT FROM AUTHOR]

We report a full dimensional ab initio-based global potential energy surface (PES) and dipole moment surface (DMS) for Cl-H2O. Both surfaces are symmetric with respect to interchange of the H atoms. The PES is a fit to thousands of electronic energies calculated using the coupled-cluster method (CCSD(T)) with a moderately large basis (aug-cc-pVTZ). The infrared spectrum and vibrational dynamics are reported and compared to experiment. These results are analyzed by examination of wave function and the dipole surface. [ABSTRACT FROM AUTHOR]

The development of spiral pattern in a model representing chlorite-iodide-malonic acid reaction is investigated theoretically and numerically. We have carried out a multiple scale analysis of the model to identify the experimentally admissible parameter range and the appropriate perturbation for shifting Hopf bifurcation boundary towards the oscillating region. Our theoretical analysis is corroborated by numerical simulation. [ABSTRACT FROM AUTHOR]

Low-lying singlet and triplet electronic excited states of ClOOCl are presented. Calculations of the excitation energies and oscillator strengths are reported using excited state coupled cluster response methods, as well as the complete active space self-consistent field method with the full Breit-Pauli spin-orbit operator. These calculations predict that for ClOOCl there should be a weakly absorbing triplet state lying below the lowest absorbing singlet excited state. This state is predicted to have an absorption maximum at about 385±25 nm. This lowest triplet state is calculated to be dissociative and leads to ClOO+Cl. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

ClSO was produced as an intermediate upon irradiating a flowing mixture of Cl[sub 2]SO and Ar with a KrF excimer laser at 248 nm. A step-scan Fourier-transform infrared spectrometer coupled with a small multipass absorption cell was employed to detect time-resolved absorption spectrum of ClSO. A transient spectrum in the region 1120–1200 cm-1, which diminished on prolonged reaction, is assigned to the S–O stretching (ν[sub 1]) mode of ClSO. A spectrum with a resolution of 0.3 cm-1 partially reveals rotational structure with the Q-branch at 1162.9 cm-1. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predict the geometry, vibrational, and rotational parameters of ClSO. An IR absorption spectrum of ClSO simulated based on predicted rotational parameters agrees satisfactorily with experimental results. ClSO produced from photolysis of Cl[sub 2]SO at 248 nm is internally hot. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Whereas conical intersections between potential energy surfaces of bound states are well known, the interaction of short-lived states has been investigated only rarely. Here, we present several systematically constructed model Hamiltonians to study the topology of intersecting complex potential energy surfaces describing short-lived states: We find the general phenomenon of doubly intersecting complex energy surfaces, i.e., there are two points instead of one as in the case of bound states where the potential energy surfaces coalesce. In addition, seams of intersections of the respective real and imaginary parts of the potential energy surfaces emanate from these two points. Using the Σ* and Π* resonance states of the chloroethene anion as a practical example, we demonstrate that our complete linear model Hamiltonian is able to reproduce all phenomena found in explicitly calculated ab initio complex potential energy surfaces. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The mechanism for the reaction ClO+ClO[sub 3] on both singlet and triplet state potential surfaces has been investigated with the modified Gaussian-2 method based on the B3LYP/6-311+G(3df ) optimized stationary-point geometries. The result shows that the barrierless association reaction producing ClOClO[sub 3] and two lower barrier O-atom abstraction reactions take place primarily on the singlet state potential surface; they are energetically more favorable than those occurring on the triplet state surface. Rate constants calculated by variational transition state and Rice–Ramsperger–Kassel–Marcus theories suggest that the major products are ClOClO[sub 3] at low temperatures (<700 K) and OClO+ClOO at high temperatures. The following rate constants are recommended for atmospheric chemistry and combustion applications: k[sub 1][sup ∞](ClOClO[sub 3])=1.43×10[sup -10] T[sup 0.094]exp(-82/T) cm[sup 3] molecule[sup -1] s[sup -1] (200–3000 K) and k[sub 1][sup 0](ClOClO[sub 3])=0.14 T[sup -10.19]exp(-1597/T) cm[sup 6] molecule[sup -2] s[sup -1] (200–800 K) for He as the third-body. In addition, a potential high-temperature reverse reaction involving Cl and ClO[sub 4] has been predicted to yield exclusively the ClO and ClO[sub 3] products; its rate constant is predicted to be: k[sub 4](ClO+ClO[sub 3])=8.05×10[sup -11] T[sup 0.158] exp(-49/T) cm[sup 3] molecule[sup -1] s[sup -1] (200–3000 K). The heats of formation at 0 K for s-ClO[sub 3], ClO[sub 4], and ClOClO[sub 3] have been predicted to be 46.7, 59.4, and 38.3 kcal/mol with about 1 kcal/mol uncertainty using the new heat of formation of OClO, 24.1±0.1 kcal/mol, based on the most recent bond dissociation energy of O–ClO reported in the literature. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The hydrogen atom abstraction reaction between Cl([sup 2]P[sub 3/2]) and ethane has been studied at a mean collision energy of 0.24 eV. The experiments were performed in a coexpansion of molecular chlorine and ethane, with the atomic Cl reactants generated by laser photodissociation of Cl[sub 2] at 355 nm. HCl(v[sup ′],j[sup ′]) products were detected quantum state selectively using (2+1) resonantly enhanced multiphoton ionization, coupled with velocity-map ion imaging. The ion images were used to determine center-of-mass angular and kinetic energy release distributions. Several analysis methods were employed and have been carefully assessed. It is shown that the single beam experiments can be used with confidence to determine both center-of-mass angular and energy release distributions. For the title reaction the angular distribution is found to be forward peaking, with on average 22% of the available energy channeled into internal excitation of the ethyl coproducts. Possible sources of this internal excitation are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on theoretical valence ionization spectra of molecules relevant in the stratosphere photochemistry obtained by all-electron SAC-CI (symmetry-adapted-cluster-configuration-interaction) calculations. Vertical ionization energies and pole strengths of the one- and two-electron processes of C1[sub 2]O and F[sub 2]O were calculated beyond the energy region so far explored in the few other available theoretical and experimental studies to interpret the electronic structure of these molecules. Early and recently proposed incomplete assignments of the available He I photoelectron spectra are discussed and completed at least up to 20-21 eV binding energy on firmer grounds relying on valuable and accurate results based on different basis sets and an adequate treatment of electron correlations. Our theoretical data predict satellite states of C1[sub 2]O starting already in the outer-valence region because of strong correlation effects; the (2b[sup -1, sub 1]), (8a[sup -1, sub 1]), and (6b[sup -1, sub 2]) states interact with the two-electron processes and they split into more-than-two peaks. On the other hand, Koopmans' picture is valid for the main peaks of F[sub 2]O and no prominent satellites with strong intensity were found in the outer-valence region. The (4b[sup -1, sub 2]), (6a[sup -1, sub 1]), and ( 1a[sup -1, sub 2]) were attributed to the second band of F[sub 2]O, for which different assignments or orderings of the states have previously been proposed in some experimental and theoretical works. Differences of the valence-ionization spectra of C1[sub 2]O and F[sub 2]O for the appearance of the satellites in the intermediate energy region have been discussed with the aid of the calculated ionization potentials and excitation energies. For C1OOC1, we have presented the first theoretical low-energy ionization spectrum and discussed the character of the calculated states referring to the available ionization spectra of C1O radical. [ABSTRACT FROM AUTHOR]

The self-reaction of ClO radicals has been investigated by ab initio molecular orbital and variational transition state theory calculations. Both singlet and triplet potential energy surfaces were predicted by the modified Gaussian-2 method. The reaction was shown to take place mainly over the singlet surface by forming ClOOCl (k[sub 1]) and ClOClO (k[sub 1[sup ′]]). These association processes were found to be strongly pressure dependent and the predicted total rate constants are in good agreement with the experimental data. The predicted second- and third-order rate constants for formation of ClOOCl and ClOClO can be expressed, respectively, in units of cm3 molecule-1 s-1 and cm6 molecule-2 s-1 by k[sub 1][sup ∞]=1.6×10[sup -9]T[sup -0.67] exp(-64/T), k[sub 1[sup ′]][sup ∞]=6.4×10[sup -9]T[sup -0.78] exp(-76/T), and k[sub 1][sup 0]=8.31×10[sup -20]T[sup -4.96] exp(-336/T), k[sub 1[sup ′]][sup 0]=1.72×10[sup -14]T[sup -6.99] exp(-926/T) in the temperature range 180–500 K for N[sub 2] as the third body. The observed T, P-dependent data could be best accounted for with the heat of formation of ClOOCl, Δ[sub f]H[sub 0][sup o](ClOOCl)=29.4±1 kcal/mol. The formation of Cl[sub 2]+O[sub 2] (2), Cl+ClOO (3), and Cl+OClO (4) products have been confirmed, with the predicted pressure-independent rate constants: k[sub 2]=1.09×10[sup -13]T[sup 0.66] exp(-1892/T); k[sub 3]=1.36×10[sup -13]T[sup 0.77]exp(-2168/T); k[sub 4]=6.26×10[sup -11]T[sup 0.005] exp(-2896/T), respectively, in units of cm3 molecule-1 s-1, covering the temperature range 200–1500 K. These results are also in reasonable agreement with existing experimental kinetic data. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photoelectron (PE) spectra of ClH[SUP-,SUB2] and ClD[SUP-,SUB2] were measured at 299 nm (4.154 eV). Photodetachment of these anions accesses the prereactive van der Waals well on the ground state Cl+ H[SUB2] potential energy surface, as well as the low-lying spin-orbit excited states resulting from the interaction of Cl and Cl* with H[SUB2]. The PE spectra are dominated by two relatively narrow peaks corresponding to transitions to the neutral Cl·H[SUB2] and Cl*· H[SUB2] complexes. The energetics and widths of these features are interpreted in terms of the properties of the anion and neutral potential energy surfaces. [ABSTRACT FROM AUTHOR]

The state-resolved and isotope-specific detection of nascent C10 generated from the photodissociation of Cl[sub 2]O parent molecules is performed by observing single-color (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm; additionally state-resolved detection of nascent Cl0 is performed by observing single-color two photon laser-induced fluorescence. The REMPI spectrum is assigned to the ClO(C² Σ[sup -],υ'=O←X²Π[sub ω], υ = 0) transition. The population of rotational states up to J = 130 is evidence of large rotational excitation induced by a strong dependence of the excited potential energy surface (PES) on the Jacobi angle γ. Formation of the ²Π[sub &frac32;] spin-orbit state is preferred: p(²Π3[sub ½]): P(²Π[sub &frac32;]) = 0.30 ± 0.05 suggesting significant radiationless transfer from the excited PES to closely lying neighboring states. The anisotropy parameter for the transition is determined to be β= 0.35 independent of the ClO quantum state. The principal excited electronic state is assigned to a ¹B[sub 2] ← ¹ A[sub 1] transition, in agreement with recent ab initio calculations. The measured β value is smaller than the limiting value of 1.0, suggesting dynamic reasons and simultaneous excitation to more than one PES. A fast and direct fragmentation process is deduced, where the upper limit for the lifetime of the excited dissociative state is calculated to be 300 fs. [ABSTRACT FROM AUTHOR]

The dissociative electron transfer reaction CH[sub 3]Cl + e[sup -] → CH[sub 3] + Cl[sup -] in aqueous solution is studied by using a QM/MM method. In this work the quantum subsystem (a methylchloride molecule plus an electron) is described using density functional theory while the solvent (300 water molecules) is described using the TIP3P classical potential. By means of molecular dynamics simulations and the thermodynamic integration technique we obtained the potential of mean force (PMF) for the carbon-chlorine bond dissociation of the neutral and radical anion species. Combining these two free energy curves we found a quadratic dependence of the activation free energy on the reaction free energy in agreement with Marcus' relationship, originally developed for electron transfer processes not involving bond breaking. We also investigated dynamical aspects by means of 60 dissociative trajectories started with the addition of an extra electron to different configurations of a methylchloride molecule in solution. The PMF shows the existence of a very fiat region, in which the system is trapped during some finite time if the quantum subsystem quickly losses its excess kinetic energy transferring it to the solvent molecules. One of the most important factors determining the effectiveness of this energy transfer seems to be the existence of close contacts (hydrogen bonds) between the solute and the solvent. [ABSTRACT FROM AUTHOR]

Measurements of dissociative electron attachment (DEA) cross sections in chloroalkanes and chlorofluoromethanes have shown strong correlations between the peak DEA cross sections and the vertical attachment energies (VAEs) of these compounds. We explore the extent to which these gas phase data can be used to predict such cross sections for molecules embedded within or on the surface of a Kr solid. Effective VAEs are computed that include polarization of the solid by the anion and effects due to electron motion in the lattice. Comparisons are made with recent surface and bulk measurements and show good agreement for CF[sub 3]C1 both within and on the surface. Satisfactory agreement is found for CH[sub 3]C1 in the bulk but not on the surface. [ABSTRACT FROM AUTHOR]

Highly inverted vibrational level populations are found for ClO fragments resulting from the UV photodissociation of OClO([sup 2]A[sub 2] ν[sub 1]>20) into ClO(X [sup 2]Π[sub Ω],v,J) and O([sup 3]P[sub J]) fragments. These distributions depend significantly on the spin-orbit J state of the oxygen O([sup 3]P[sub J]) partner atom. In contrast, the ClO rotational excitation is modest. Distinct rotational structure is visible in the O ([sup 3]P[sub J]) photofragment yield spectrum recorded from the highly excited OClO ([sup 2]A[sub 2] ν[sub 1]=21) vibronic band, which is indicative for hitherto unforeseen long dissociation lifetimes of very highly excited OClO. The data point towards an unexpected nearly-linear and highly asymmetric dissociation geometry. Carrying out near-threshold fragmentation experiments of OClO ([sup 2]A[sub 2]0,0,0)→ClO (X [sup 2]Π[sub 3/2] v=0, J)+O([sup 3]P[sub 2,1,0]) the dissociation energy D[sub 0] of OClO has been accurately determined to 247.3±0.5 kJ/mol. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the electronic structure of chlorine oxide radicals. Use of anion photoelectron spectroscopy for the study; Electron affinities of ClO[sub 3] and ClO[sub 4]; Comparison of photoelectron with available theoretical calculations.

Focuses on a theoretical study on the excited states of methylhypochlorite using high level ab initio molecular orbital methods. Use of multireference configuration interaction method in calculating the vertical excitation energies; Examination of potential energy curves for the lowest eight states.

Studies the microwave spectra of the normal isotopic species of N-chlorodifluoromethanimine. Types of coupling constants; Matrix elements; Structural properties; Spectroscopic constants; Energy level of the hyperfine pattern; Quartic centrifugal distortion contants.

Studies the combined reaction and vapor-liquid equilibrium of Br[sub 2]+Cl[sub 2]+BrCl system using the reaction ensemble Monte Carlo. Modeling of the substances as nonpolar and dipolar two-site Lennard-Jones molecules with Lorentz-Berthelot mixing rules for unlike atoms; Calculation of the complete phase compositions.

The three-dimensional ground state potential energy surfaces for He-Cl[SUB2], Ne-C1[SUB2], and Ar-C1[SUB2] have been calculated using the single and double excitation coupled-cluster approach with noniterative perturbational treatment of triple excitations [CCSD(T)]. Calculations have been performed with the augmented correlation consistent triple zeta basis sets supplemented with an additional set of bond functions. Single point calculations for approximate minima have also been performed with several other basis sets including the quadruple zeta basis set (aug-cc-pVQZ) with bond functions. For He-C1[SUB2] and Ar-C1[SUB2] the CCSD(T) results show that the linear configuration is lower in energy than the T-shaped one. For Ne-C1[SUB2] the CCSD(T) approach predicts the T-shaped configuration to be lower in energy. The linear configuration has been found to be more sensitive than the T-shaped one to the changes of the C1-C1 bond length with the interaction becoming weaker when the C1-C1 bond length is shortened from its equilibrium value and stronger when it is lengthened. More detailed analysis shows that sensitivity of component energies such as exchange, dispersion, and induction is much greater than that of supermolecule results. The interaction in the T-shaped configuration becomes slightly stronger for shorter C1-C1 bonds. For He-C1[SUB2] and Ar-C1[SUB2] the larger zero-point vibrational energy of the linear configuration is responsible for making the T-shaped configuration the ground vibrational state. Vibrational effects further increase the difference in energy between the ground state T-shaped configuration of Ne-C1[SUB2] and its linear counterpart. [ABSTRACT FROM AUTHOR]

Presents a quantum dynamics study of the Cl+CH[sub 4]...HCl+CH[sub 3] reaction using a four-dimensional rotating bond umbrella model. Hamiltonian and coupled channel equations; Hyperspherical projection method; Surface functions; Guided spectral transform Lanczos method; Evaluation of the surface Hamiltonian.

Studies the photodissociation of sulfur-chlorine compounds and sulfur-sulfur bonds by translational photolysis. Dissociation channels undergone by the compound to form the products; Determination of the relative yield; Detection of two separate product translational energy distributions.

Examines the reaction of atomic chlorine with methane using resonance-enhanced multiphoton ionization. Indication of possible reaction of spin-orbit excited chlorine; Vibrations created by large enhancements in reactivity; Importance of vibrationally excited reagents to thermal kinetics of the reaction of chlorine with methane.

The (1+1′)+1 resonance enhanced multiphoton ionization (REMPI) spectrum of jet-cooled CS2 has been recorded in the 61 000–65 600 cm-1 excitation energy range. Four prominent band groups are observed that can be assigned to Δν2=-1 and Δν2=1 sequences of the two-photon electronically forbidden 4p 1,3Δu←X 1Σ+g transitions. Weak bands to higher energy appear to be associated with the 310, 230 and 110210 bands and corresponding sequence bands. The results show that the upper states are not 3d Rydberg states as has been previously supposed, and are consistent with a recent reinvestigation of the corresponding (3+1) REMPI spectrum. Further experimental information is obtained on the anomalous vibrational band structure of transitions to the 3Δu state. The 201 and 212 bands of the 4p 1Πu←X 1Σ+g transition are also observed, but are much weaker, suggesting that vibronic interactions are less important in this state compared to the 4p 1,3Δu states. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structure of ClO2 has been calculated for the X 2A‘ ground state using unrestricted Hartree–Fock (UHF), unrestricted second-order Mo/ller–Plesset perturbation (UMP2), configuration interaction using single and double excitation (CISD), and quadratic configuration interaction (QCI) ab initio molecular orbital methods. Calculations using UMP2 and CISD wave functions predict a ClO bond length of 1.728±0.01 Å. The single-configuration based QCI in the singles and doubles space with perturbation inclusion of triple substitutions, denoted QCISD(T), yield a ClO bond length of 2.205 Å. The QCI results are consistent with results of Jensen who showed that the ClO bond length is 2.181 Å using annihilated self-consistent methods (AUMP2). The thermochemistry of ClO2 radical has been calculated using MP2 and QCI methods using an isodesmic scheme. Our scheme predicts the heat of formation for ClO2 at 0 K to be 24.6±2 kcal mol-1. [ABSTRACT FROM AUTHOR]