Showing papers on "Potential energy surface published in 1990"
TL;DR: In this article, the authors present a theoretical model for stimulated desorption due to the interaction of energetic substrate carriers with molecular adsorbates based on the premise that optically excited hot electrons scatter into an unoccupied valence electron resonance of the adsorbate, thus forming a temporary negative molecular ion which then experiences an enhanced attraction towards the substrate Neutralization of the ion returns the adsorbed molecule to one of the potential energy surface, possibly in an internally excited state.
252 citations
TL;DR: In this article, a single-valued potential energy surface for the ground state of HO{sub 2} from the double many-body expansion (DMBE) method was reported.
Abstract: The authors report a new single-valued potential energy surface for the ground state of HO{sub 2} from the double many-body expansion (DMBE) method. This new surface conforms with the three-body energy of recent ab initio CAS SCF/CCI calculations semiempirically corrected by the DMBE-SEC method and reproduces the most accurate estimates of the experimental dissociation energy, equilibrium geometry, and quadratic force constants for the hydroperoxyl radical. Using this new HO{sub 2} (DMBE IV) potential energy function, exploratory dynamics calculations of the O + OH {yields} O{sub 2} + H reaction have also been carried out by the quasiclassical trajectory method. Thermal rate coefficients are reported for T = 250, 1,250, and 2,250 K that are shown to be in good agreement with the best reported measurements.
242 citations
TL;DR: In this article, a new and improved version of the technique of H atom photofragment translational spectroscopy has been applied to a study of H2S photodissociation at 121.6 nm.
Abstract: A new and improved version of the technique of H atom photofragment translational spectroscopy has been applied to a study of H2S photodissociation at 121.6 nm. The primary fragmentation pathways leading to H+SH(A) fragments and H+H+S(1D) atoms are observed to dominate the product yield; the yield of H atoms formed in conjunction with ground state SH(X) fragments is undetectably small. The majority of the SH(A) fragments are formed in their v=0 level with a rotational state population distribution that spans all possible bound and quasibound rotational levels. The experimental determination of the energies of these hitherto unobserved high rotational states has enabled a refinement of the SH(A) potential energy function, an improved estimate of the SH(A) well depth (9280±600 cm−1), and thus of the SH(X) ground state bond dissociation energy D00 (S–H)=3.71±0.07 eV. All aspects of the observed energy disposal in the title photodissociation process may be understood, qualitatively, if it is assumed that (i) the primary fragmentations occur on the B 1A1 potential energy surface and (ii) Flouquet’s ab initio calculations of portions of this surface [Chem. Phys. 13, 257 (1976)] correctly predict its gross topological features.
234 citations
TL;DR: In this article, the authors show how ab initio quantum chemistry methods recently developed for calculating anharmonic constants about a potential minimum can be readily adapted to obtain those related to a transition state, thus providing a rigorous and practical way to apply this non-separable transition state theory.
219 citations
TL;DR: In this paper, the activation energy, Ea, can be related approximately to the barrier height in the potential energy surface for the reaction, where Ea is defined as the ratio of activation energy to barrier height.
Abstract: where the activation energy, Ea, can be related approximately to the barrier height in the potential energy surface for the reaction. What is not generally realized is that there are many simple reactions of wide current importance that do not have rate constants of this form and, indeed, have rate con stants that decrease in magnitude when the temperature is increased (1-4). These reactions can have rate constants that are orders of magnitude larger than those obtained for reactions with activation energies, and it has not been easy to make accurate measurements of their rate constants, as highly reactive species such as free radicals and ions are usually involved. Furthermore, the rate constants can show interesting temperature depen dences, which can also be hard to measure, especially for low temperatures (1). Due to significant improvements in techniques, however, some of these difficulties are being overcome and a wealth of experimental data is now being produced on the rates of fast chemical reactions that appear to have zero or negative activation energies (1, 2). This advance has come about not only through the sophisticated use of laser and mass-spectrometric
215 citations
TL;DR: In this paper, the potential energy surfaces of the van der Waals complex of OH+Ar have been calculated using the coupled electron pair approximation (CEPA) and a very large basis set.
Abstract: The potential energy surfaces of OH+Ar, which correlate asymptotically with OH(X 2Π)+Ar(1S) and OH(A 2Σ+)+Ar(1S), have been calculated using the coupled electron pair approximation (CEPA) and a very large basis set. The OH–Ar van der Waals complex is found to be bound by about 100 cm−1 in the electronic ground state. In agreement with several recent experimental studies the first excited state is found to be much more stable. The A state potential energy surface has two minima at collinear geometries which correspond to isomeric OH–Ar and Ar–OH structures. The dissociation energies De are calculated to be 1100 and 1000 cm−1, respectively; both forms are separated by a barrier of about 1000 cm−1. The equilibrium distances for OH–Ar and Ar–OH are calculated to be 2.9 and 2.2 A, respectively, relative to the center of mass of OH. In order to investigate the nature of the strong binding in the A state, we have calculated accurate dipole and quadrupole moments as well as dipole and quadrupole polarizabilities ...
206 citations
TL;DR: In this article, an investigation of melting, freezing, and coexistence phenomena for small clusters using Ar7, Ar8, Ar13, and Ar14 as specific representative examples is presented.
Abstract: An investigation of melting, freezing, and coexistence phenomena is presented for small clusters using Ar7, Ar8, Ar13, and Ar14 as specific representative examples. Combining the results of molecular dynamics simulations, especially short‐time kinetic energy averages and quenching, with accurate calculations of the local minima and transition states illuminates the relationship between the potential energy surface and dynamical processes. The results are consistent with a recent general defect theory of melting.
179 citations
TL;DR: In this paper, the Hamiltonian of the ArHCl (HCl; ν=0) van der Waals (vdW) molecule was evaluated in the discrete variable representation (DVR) of the stretch and bend internal vibrational basis and a basis of parity adapted rotation functions.
Abstract: The ArHCl (HCl; ν=0) van der Waals (vdW) molecule has a large number of bound and rotationally predissociative (resonance) states for total angular momentum in the range of 0≤J≤60. Using the Jacobi coordinates and the total angular momentum representation in the body‐fixed reference frame, the Hamiltonian is evaluated in the discrete variable representation (DVR) of the stretch and bend internal vibrational basis and a basis of parity adapted rotation functions. The facile and effective application of the DVR is greatly enhanced by an appropriate choice of the basis set. The sequential diagonalization and truncation of the Hamiltonian permit accurate and efficient determination of eigenstates. Using Hutson’s H6 potential energy surface, the energies and wave functions of all bound and resonance states are computed for selected J’s up to J=60. A novel flux projection technique facilitates semiquantitative evaluation of the lifetimes of all states and, in particular, the simple identification of the resonance states in the L 2 eigenvector basis.
175 citations
TL;DR: In this article, the authors measured the dissociative chemisorption probability at zero surface coverage S0 for D2(H2) on Pt(111) terraces as a function of initial energy Ei, angle of incidence θi, surface temperature Ts, isotopic mass and nozzle temperature Tn.
Abstract: Molecular beam techniques have been utilized to measure the dissociative chemisorption probability at zero surface coverage S0 for D2(H2) on Pt(111) as a function of initial energy Ei, angle of incidence θi, surface temperature Ts, isotopic mass and nozzle temperature Tn. S0 shows a large increase with translational energy, but no threshold in Ei, a peaking at θi=0°, and an independence with Ts, isotope and Tn. These results are interpreted in terms of direct dissociative chemisorption on the Pt(111) terraces. The dynamical picture that emerges is that although there is no significant barrier to dissociation along the minimum energy path, barriers do exist along nonoptimal reactive trajectories. Thus, the ‘‘translational activation’’ and other dynamical observations are intimately related to the multidimensional aspects of the dissociative potential energy surface. Some aspects of the dissociative chemisorption, however, still seem somewhat surprising within this general description.
166 citations
TL;DR: In this paper, the authors present a theoretical study of the dissociative adsorption of hydrogen molecules from a series of model potential energy surfaces, where a quantum wave packet is chosen to represent the molecule and the dynamics are solved by a spectral grid method.
Abstract: In this work we present a theoretical study of the dissociative adsorption of hydrogen molecules from a series of model potential energy surfaces. The aim is to discover those particular topological features in the potential surface which are responsible for determining the vibrational state‐to‐state cross sections in both the dissociated and the scattered flux. The potential energy surface is two‐dimensional, and is chosen to be deliberately simple; a combination of Morse potentials and a Gaussian barrier. A quantum wave packet is chosen to represent the molecule and the dynamics are solved by a spectral grid method. Results show that the location of the barrier influences the scattering cross sections markedly. Early barriers result in vibrationally excited adsorbed species while late barriers produce translationally hot atoms. The individual state distributions resulting from the two model potentials are quite different. In addition, results are given for a potential where the activation barrier is deep in the exit channel. For this case, results show that molecules can trap near the barrier for significant times without invoking substrate degrees of freedom. This is explained in terms of trapping in dynamic wells. Finally, we assess the effect on dissociation probability following vibrational excitation of the hydrogen molecule.
164 citations
TL;DR: In this article, Monte Carlo simulations were performed in order to study the ordered structures formed by CO on Pt{111] at high coverage, and the results were compared with LEED and infrared (IR) spectra.
Abstract: We have performed Monte Carlo simulations in order to study the ordered structures formed by CO on Pt{111} at high coverage The results are compared with LEED and infrared (IR) spectra The calculations are based on a recently constructed potential energy surface for CO on Pt{111} and a CO–CO interaction potential deduced from the variation of the CO binding energy with coverage Ordered adsorbate structures are obtained at θ=05, 06, 067, and 071 in the simulations The so‐called compression structures (θ>05) are stabilized by the energy lowering which results when CO molecules at the high density domain walls move away from the on‐top sites because of the unbalanced repulsive CO–CO interactions If this relaxation channel is blocked, disordered adsorbate structures occur We present the resulting (θ, T) phase diagram and discuss its qualitative properties The LEED data show ordered structures at θ=05, 06, and 071, but, in contrast to previous results, or perhaps to the interpretation thereof, not at θ=067 The IR data show that the compression structures still consist of CO molecules adsorbed on distinct surface sites Finally, we discuss the changes in adsorbate structures which would result from variations in the CO–substrate potential energy surface and, in the light of these results, briefly look at the Cu{111}–CO, Ni{111}–CO, and Pd{111}–CO chemisorption systems
TL;DR: In this paper, the singlet potential energy surface of Si 2 H 2 has been explored by using ab initio theoretical methods and complete geometry optimizations and vibrational frequency analyses were performed for 11 different structural isomers at the self-consistent field (SCF) and single and double excitation configuration interaction (CISD) levels of theory using double-ζ plus polarization (DZP) and triple-ε plus double polarization (TZ2P) basis sets.
Abstract: The singlet potential energy surface of Si 2 H 2 has been explored by using ab initio theoretical methods. Complete geometry optimizations and vibrational frequency analyses were performed for 11 different structural isomers at the self-consistent field (SCF) and single and double excitation configuration interaction (CISD) levels of theory using double-ζ plus polarization (DZP) and triple-ζ plus double polarization (TZ2P) basis sets. Several extended basis sets including diffuse and higher angular momentum functions were employed in determining the final energetics of this system. Our analysis of the potential energy surface confirms that the global minimum is a C 2υ dibridged structure and reveals two minima and three transition states in the range 10-15 kcal/mol above the dibridged
TL;DR: In this paper, the authors developed the use of Delves' hyperspherical coordinates to study the reactive scattering of four-atom systems within the collinear approximation and found that HCN product vibrational states with the C-H stretch excited are produced preferentially in the reaction.
Abstract: We develop the use of Delves’ hyperspherical coordinates to study the reactive scattering of four‐atom systems within the collinear approximation. We present quantum mechanical calculations of reaction probabilities for the collinear exothermic reaction H2+CN →H+HCN. We use a potential energy surface which reproduces the essential characteristics of the reaction. The effect of freezing the CN bondlength to its equilibrium value during the reaction is also investigated and is found to be a good approximation. It is found that HCN product vibrational states with the C–H stretch excited are produced preferentially in the reaction.
TL;DR: In this article, an analytical potential energy surface for CO-CO was constructed by means of ab initio calculations for the electrostatic and first-order exchange interactions and by the use of accurate dispersion coefficients recently calculated in our group.
Abstract: We have constructed an analytical potential energy surface for CO–CO by means of ab initio calculations for the electrostatic and first‐order exchange interactions and by the use of accurate dispersion coefficients recently calculated in our group. Parameter‐free damping functions account for second‐order exchange and penetration effects. The anisotropy of this potential is represented by an expansion in spherical harmonics for the molecules A and B, up to LA, LB=5 inclusive. The second virial coefficients calculated with this potential, including quantum corrections, lie within the experimental error bars over a wide temperature range.
TL;DR: In this paper, a model for the vibrational states of atom-asymmetric top van der Waals complexes is developed, based on hindered rotation of the asymmetric top in the complex.
Abstract: A model for the vibrational states of atom–asymmetric top van der Waals complexes is developed, based on hindered rotation of the asymmetric top in the complex. The pattern of energy levels expected from such a model is described, and the dependence of the spectrum on features of the potential energy surface is explored. The selection rules arising from the model are presented. The model is used to interpret the infrared spectra of Ar–H2O reported by Cohen et al. [J. Chem. Phys. 89, 4494 (1988)], and preliminary information on the effective bending potential for Ar–H2O is obtained. The potential is very isotropic, varying by only about 40 cm−1 as a function of the angular coordinates. Predictions of band origins for other allowed infrared transitions are given.
TL;DR: In this article, Hayes-Stone Intermolecular Perturbation Theory (IMPT) was used to study the variation with distance and orientation of the various components of the interaction energy of the N H O = C hydrogen bonded trans-formamide/formaldehyde complex, a model system for hydrogen bonding in proteins.
Abstract: We have used Hayes-Stone Intermolecular Perturbation Theory (IMPT) to study the variation with distance and orientation of the various components of the interaction energy of the N H…O = C hydrogen bonded trans- formamide/formaldehyde complex, a model system for hydrogen bonding in proteins. The directionality of the total interaction energy is similar to that of the electrostatic component alone. We have analysed our data in terms of two model atom-atom intermolecular potentials, using an isotropic functional form and an anisotropic one. The anisotropic form gives an excellent representation of the IMPT potential energy surface, considerably better than the isotropic model, and is comprised entirely of theoretically justified, physically meaningful terms.
TL;DR: In this paper, a quantum wave packet calculation for the activated dissociative adsorption of H2 is presented, where the motion of the molecule is restricted to lie within a plane normal to the surface.
Abstract: A quantum wave packet calculation for the activated dissociative adsorption of H2 is presented. Restricting the motion of the molecule to lie within a plane normal to the surface we have treated all four molecular degrees of freedom exactly. We compare results obtained using two‐, three‐, and four‐dimensional simulations on the same potential and show that by restricting the molecular orientation, important dynamical effects are lost. The potential employed in the calculations has been obtained using the effective medium approximation. In the simulations it has been possible to treat dissociation, rotations and diffraction on an equal footing. By including a rotational degree of freedom, it is seen that strong orientational effects occur near to the transition state and result in an anisotropic selectivity in the dissociation. By examining the state‐to‐state scattering probabilities, it is possible to use the nonreacting (scattered) fraction to provide information on the reactive potential energy surface.
TL;DR: In this article, a 3D coupled channel calculation for total angular momentum J = 0 for the reaction F+H2→HF+H using a realistic potential energy surface is analyzed.
Abstract: Accurate 3D coupled channel calculations for total angular momentum J=0 for the reaction F+H2→HF+H using a realistic potential energy surface are analyzed The reactive scattering is formulated using the hyperspherical (APH) coordinates of Pack and Parker The adiabatic basis functions are generated quite efficiently using the discrete variable representation method Reaction probabilities for relative collision energies of up to 174 kcal/mol are presented To aid in the interpretation of the resonances and quantum structure observed in the calculated reaction probabilities, we analyze the phases of the S matrix transition elements, Argand diagrams, time delays and eigenlifetimes of the collision lifetime matrix Collinear (1D) and reduced dimensional 3D bending corrected rotating linear model (BCRLM) calculations are presented and compared with the accurate 3D calculations
TL;DR: In this article, the authors analyzed the linear H⊗(g⊕2h) Jahn-Teller problem with respect to the instability of icosahedral molecules in fivefold degenerate states.
Abstract: The linear H⊗(g⊕2h) Jahn–Teller problem, relevant to the instability of icosahedral molecules in fivefold degenerate states, is analyzed in detail for the first time. The method of the isostationary function is used to identify all the extrema of the corresponding potential energy surface. Depending on one single mode‐splitting parameter, two different coupling regimes are possible, favoring either pentagonal or trigonal minima. The saddle points on interconversion paths between equivalent minima are identified and the topology of the low‐energy regions of the surface is determined. The results are found to be in agreement with the epikernel principle. In addition the symmetry characteristics of the principal warping term under the SO(5) symmetry group of electronic space are assigned.
TL;DR: In this article, three-dimensional quantum mechanical calculations for photofragmentation of the Ne ICl van der Waals molecule in the energy region of the electronically excited B(3∏0+) state of ICl are presented and compared with experiments.
Abstract: Converged three‐dimensional quantum mechanical calculations for photofragmentation of the Ne⋅⋅ICl van der Waals molecule in the energy region of the electronically excited B(3∏0+) state of ICl are presented and compared with experiments. Lifetimes and final state distributions for the ICl fragments were determined for vibrational predissociation from the lowest van der Waals level in the B(v’=2) channel. Good agreement between theory and experiment was achieved using a sum of atom–atom pairwise potentials. This potential energy surface predicts the equilibrium geometry of the complex to be bent at 140° with the Ne atom towards the Cl end of ICl. The diabatic vibrational golden rule (DVGR) approximation, as well as the rotational infinite order sudden approximation (RIOSA), have been tested again the full 3D calculations. Analysis of the quasibound wave function reveals that the highly inverted rotational distribution of the ICl fragments observed in the experiment, is not due to zero‐point bending motion....
TL;DR: In this paper, the authors used Semiclassical variational transition state theory to calculate the gas-phase rate coefficient and to determine a semi-empirical value of the barrier height to reproduce the experimental value of this coefficient at 300 K.
Abstract: Correlated calculations (MP2/6-31G**) of the energies and frequencies at the saddle point, ion-dipole complex, and reactants plus additional energy calculations at selected geometries in the strong interaction region are used to parameterize a multidimensional potential energy function for the title reaction. Semiclassical variational transition-state theory is used to calculate the gas-phase rate coefficient and to determine a semiempirical value of the barrier height to reproduce the experimental value of this coefficient at 300 K. The semiempirical gas-phase barrier height is 3.1 kcal/mol. A new potential energy function with this barrier height is created and used to calculate the temperature-dependent rate coefficients and phenomenological activation energies for both CH{sub 3}Cl and CD{sub 3}Cl over the 200-1,000 K temperature range. The activation energy is predicted to show a large temperature dependence. The kinetic isotope effect is predicted to be 1.04 at room temperature.
TL;DR: In this paper, the potential energy surface of liquid water has been investigated in terms of vibrational mode excitations at its local energy minima, called inherent structures, which are the source of the water binding structural reorganization dynamics.
Abstract: Dynamical behavior of liquid water is investigated by analyzing the potential energy surface involved. Multidimensional properties of the potential energy surface are explored in terms of vibrational mode excitations at its local energy minima, called inherent structures. The vibrational mode dynamics, especially mechanism of mode relaxation and structure transitions, is analyzed. It shows very strong excitation energy dependence and mode dependence. There are three kinds of vibrational coupling among modes. For excitations of energy near the room temperature, most modes (more than 90% of total modes) individually interact with only one or two other modes, and yield near recurrence of the mode energy in a few tens picoseconds (very slow relaxation). Spatially localized modes in the intermediate frequency range couple with many delocalized modes, yielding fast relaxation. The coupling is governed by atomic displacement overlaps and frequency matching. Each mode couples with nearby frequency or double frequency modes through the Fermi resonance. Lowest frequency modes almost always lead to transitions from a potential energy well to neighbor potential wells, called inherent structure transitions. In high energy excitation, some intermediate frequency modes also yield such transitions. There exist very low energy paths involving single or few water molecule displacements at almost every inherent structure, indicating that certain facile molecular movements occur even in very low temperature states. Different energy excitations of a low frequency mode result in different inherent structure transitions; transitions caused by high energy excitations involve many large molecular displacements. These inherent structure transitions are the source of the water binding structural reorganization dynamics. Significance of these vibrational mode dynamics in the water dynamics is discussed.
TL;DR: Weiner et al. as mentioned in this paper applied the technique of H(D) atom photofragment translational spectroscopy to the photodissociation of H2S(D2S) following excitation at a number of wavelengths in its first absorption continuum.
Abstract: The technique of H(D) atom photofragment translational spectroscopy has been applied to the photodissociation of H2S(D2S) following excitation at a number of wavelengths in its first absorption continuum. The respective bond dissociation energies were determined as D0(H–SH)=3.90±0.03 eV and D0(D–SD)=4.00±0.02 eV. The measured vibrational energy disposal in the partner ground state SH(SD) fragments and the product angular distributions support and extend the earlier results of van Veen et al. [Chem. Phys. 74, 261 (1983)], while the deduced rotational and spin–orbit state population distributions in these fragments appear to be generally consistent with the recent measurements of Weiner et al. [J. Chem. Phys. 90, 1403 (1989)]. We present a schematic adiabatic potential energy surface for the dissociative 1A‘ excited state via which it is possible to rationalize virtually all existing dynamical measurements relating to this fragmentation process.
TL;DR: In this article, the internal coordinates of the disaccharide Man-α(1 → 3)-Man-α-O-Me were relaxed and minimized through an extensive molecular mechanics scheme.
Abstract: We report calculations of potential energy surfaces where all the internal coordinates of the disaccharide Man-α(1 → 3)-Man-α-O-Me were relaxed and minimized through an extensive molecular mechanics scheme. Flexibility within the mannopyranose rings plays a crucial role. Introduction of the relaxed principle into the conformational description of the disaccharide does not greatly alter the overall shape of the low-energy domains but it reveals new local minima. However, its principle effect is the lowering of energy barriers in the potential energy surface. New conformational transitions about the glycosidic bonds appear, permiting pathways among the low energy sections. This occurs with only little variation of the classical 4C1 conformation of the mannopyranose residues. All the conformations observed in the solid state, along with those already predicted through the joint use of NMR and modeling techniques, fall into the populations of stable conformers calculated in the present work. Moreover, a satisfactory agreement is reached between previously observed NOE values, and the theoretical one, calculated from the averaging of more than 500 microstates. The present results reconciliate most of the apparently conflicting data previously reported; they provide strong support for the application of the concept of conformational averaging to solution behavior. Some limitations of the proposed methodology are also discussed.
TL;DR: In this paper, an ab initio potential energy surface has been computed using the coupled electron pair approximation with a large basis set, and the rovibrational bound states for the complexes are calculated using a variational method.
Abstract: Calculations of spectra for the excitation of the van der Waals modes in the weakly bound complexes H2HF, D2HF, and H2DF are reported. An ab initio potential energy surface has been computed using the coupled electron pair approximation with a large basis set. The rovibrational bound states for the complexes are calculated using a variational method. A self‐consistent field approach is used to optimize the basis sets for bending and stretching motion in the van der Waals complex. The calculated spectra compare very well with those measured in near‐infrared experiments. The computations provide a systematic analysis of the relative stability and rigidity of the different complexes, the very large zero‐point energy effects, and the unusual nature of the rovibrational wave functions in these van der Waals molecules. The predicted spectra contain some new bands with surprisingly large intensities that might be detectable in experiments.
TL;DR: In this article, a set of anharmonic vibrational constants was derived, unifying the SEP data reported here with previous infrared and overtone data, which is expected to be able to predict the position of normal mode states below 19 000 cm−1 with an accuracy within 3 cm −1.
Abstract: Stimulated-emission pumping (SEP) spectra of HCN have been measured by using a pulsed, tunable argon fluoride laser with a frequency-doubled, pulsed dye laser. Sixty-seven vibrational states of the ground electronic state between 8 900 and 18 900 cm−1 have been observed. Eighty percent of the states can be described within a traditional normal mode context. A full set of anharmonic vibrational constants was derived, unifying the SEP data reported here with previous infrared and overtone data. This set of molecular constants is expected to be able to predict the position of normal mode states below 19 000 cm−1 with an accuracy within 3 cm−1. Twenty percent of the states could not be assigned to unperturbed normal mode states, and a systematic analysis was performed in an attempt to find a simple explanation for them based on possible perturbations. Except for the lowest energies, no simple explanation was found, suggesting that delocalized isomerizing vibrational states are playing a role in the observed vibrational structure at higher energy. Direct comparison with assigned normal mode states derived from quantum-mechanical vibrational-structure calculations on the only available three-dimensional potential energy surface were made possible by these experiments. The deviation between experiment and theory as a function of the number of bending quanta, the vibrational motion that couples strongly to the isomerization reaction coordinate, makes clear that the isomerization barrier height is too low on this surface. The present state of experimental characterization of the HCN system should be good enough to permit a high-quality potential energy surface to be derived for highly vibrationally excited HCN.
TL;DR: In this paper, the photoelectron spectra of the ions BrHI−, ClHI− and FHI− along with their deuterated counterparts are presented, providing information on the transition state region of the potential energy surfaces describing the exothermic neutral reactions X+HI→HX+I(X=Br, Cl, F).
Abstract: The photoelectron spectra of the ions BrHI−, ClHI−, and FHI−, along with their deuterated counterparts, are presented. These spectra provide information on the transition state region of the potential energy surfaces describing the exothermic neutral reactions X+HI→HX+I(X=Br, Cl, F). Vibrational structure is observed in the BrHI− and ClHI− spectra that corresponds to hydrogen atom motion in the dissociating neutral complex. Transitions to electronically excited potential energy surfaces that correlate to HX+I(2P3/2,2P1/2) products are also observed. A one‐dimensional analysis is used to understand the appearance of each spectrum. The BrHI− spectrum is compared to a two‐dimensional simulation performed using time‐dependent wave packet propagation on a model Br+HI potential energy surface.
TL;DR: In this article, an ab initio potential energy surface is used and the rovibrational states are calculated using a basis set method which couples the electronic spin and orbital angular momentum of the diatomic fragment with the overall rotations and vibrations of the complex.
Abstract: We calculate the rovibrational structure for the electronic transition of the Ar–OH complex between the ground and first excited electronic states, which correlate asymptotically with Ar(1S0)+OH(X 2Π) and Ar(1S0)+OH(A 2Σ+), respectively. An ab initio potential energy surface is used and the rovibrational states are calculated using a basis set method which couples the electronic spin and orbital angular momentum of the diatomic fragment with the overall rotations and vibrations of the complex. The calculated spectrum is compared with experimental results. In the low‐frequency region the spectrum is found to be well ordered and assignment of spectroscopic features in terms of bending and stretching quantum numbers is possible. Close to dissociation, bend–stretch coupling leads to highly mixed states for which such assignments are no longer possible.
TL;DR: Theoretical studies of the potential energy surface of a poorly understood allotrope of elemental sulfur, S{sub 4}, have been performed with use of ab initio electronic structure theory as mentioned in this paper.
Abstract: Theoretical studies of the potential energy surface of a poorly understood allotrope of elemental sulfur, S{sub 4}, have been performed with use of ab initio electronic structure theory. Eleven different isomers have been considered. Singlet states have been studied with SCF, two-configuration SCF (TCSCF), CISD (single and double excitation configuration interaction), and TC-CISD levels of theory, and selected triplet states have also been investigated with SCF and CISD theory. A few studies have also been performed on the most stable isomers with MR (multi-reference)-CISD, CCSD (coupled cluster theory with single and double substitution), and CCSDT-1 (CCSD with linearized triple substitutions) methods. Two basis sets, of double-{zeta} plus polarization (DZP) and triple-{zeta} plus double polarization (TZ2P) quality, respectively, have been used.The effects of f-functions on the S-S bond have been investigated with S{sub 2} as an example with a TZ2P+f basis set. Harmonic vibrational frequencies, infrared, and some Raman intensities have been evaluated, as have the ionization energies and the lowest energy electronic transitions for the most stable isomers. Experimental data for these properties are compared with the authors theoretical results.