Showing papers on "Potential energy surface published in 1979"
01 Jan 1979
TL;DR: In this paper, an extension of the classical trajectory methods for calculating inelastic scattering cross sections is presented. But the authors are careful not to overinterpret the reaction by a trajectory study because many reaction attributes depend sensitively on quantitative and qualitative features of the potential energy surfaces which are not quantitatively understood.
Abstract: Classical trajectory methods for calculating inelastic scattering cross sections are covered in earlier chapters of this book, especially Chapters 10 and 12 This chapter covers the extension of this technique to treat reactive scattering The first question which must be answered in a classical trajectory study of a reactive system is whether one should be using this method at all Classical trajectory studies are useful not just because they yield reaction cross sections, angular distributions, reactivity as a function of initial and final energy distribution, and other observable reaction at-tributes, but also for the insight they may offer into the actual reaction event One may look at the atomic motions in representative trajectories, and one may calculate such nonobservables as opacity functions (probability of reaction as a function of impact parameter) and dependence on features of the potential energy surface But one must be careful not to overinterpret the reaction by a trajectory study Because many reaction attributes depend sensitively on quantitative and qualitative features of the potential energy surfaces which are not quantitatively understood, one must be cautious about believing that the dynamical details of a particular trajectory calculation are in general accord with reality Trajectory calculations are discussed from this point of view in Chapter 18 of this book
293 citations
TL;DR: In this paper, coupled cluster doubles and manybody perturbation theory (MBPT) and coupled cluster methods are employed in an investigation of the potential energy surface of H2O in the vicinity of its equilibrium geometry.
Abstract: Many‐body perturbation theory (MBPT) and coupled cluster methods are employed in an investigation of the potential energy surface of H2O in the vicinity of its equilibrium geometry. The basis set of 39 Slater‐type orbitals is the same as that previously used in a configuration interaction study (limited to all single and double excitations, SD‐CI) of this surface, and is capable of accounting for 80% of the total correlation energy of the molecule. Detailed comparisons among the results of the various methods are presented, with particular reference to the role of size extensivity in providing a reliable model for the prediction of the shape of the surface. The predicted quartic force field obtained by the coupled cluster doubles (CCD) and by several MBPT models is in very good agreement with experiment. The inclusion of quadruple excitations, which account for about 5% of the correlation energy, is found to have a significant effect on the shape of the surface, bringing the predicted force field into sub...
225 citations
TL;DR: In this article, a gradient procedure was used to locate and to characterize both equilibrium and transition state geometries of the S0 potential energy surface of formaldehyde relevant to its dissociation to molecular products, H2+CO, to radical formation, H + HCO, and to rearrangement to hydroxycarbene, HCOH, have been studied by means of ab initio calculations.
Abstract: Features of the S0 potential energy surface of formaldehyde relevant to its dissociation to molecular products, H2+CO, to radical formation, H + HCO, and to rearrangement to hydroxycarbene, HCOH, have been studied by means of ab initio calculations. A gradient procedure was used to locate and to characterize both equilibrium and transition state geometries. Basis sets of at least double zeta (DZ) quality were employed throughout and many calculations involved more flexible basis sets including polarization functions. Force constants, normal modes and vibrational frequencies were calculated at the SCF level for stationary points on the surface. Extensive configuration interaction (CI) calculations were also carried out. For the molecular dissociation the energy barrier including the effects of polarization functions and electron correlation was 4.06 eV (93.6 kcal mole−1, 32 700cm−1). Correcting for changes in zero point vibrational energy gave an approximate activation energy of 3.76 eV (87 kcal mole−1, 30...
178 citations
TL;DR: In this article, the potential energy surface for HO 2 → HO * 2 − OH + O reaction has been calculated using the MC SCF Cl method using the multi-configuration self-consistent field configuration interaction (MCSCF Cl) method.
158 citations
TL;DR: In this paper, a review of the recent progress in reactive molecular collision calculations is reviewed, including the classification of theories of reactive scattering, the accuracy of ab initio potential energy surface calculations, global and local methods for fitting ab-i-ion potential energy surfaces in a form useful for scattering calculations, and recent developments in exact and approximate quantum, semiclassical and classical theories of chemical reactions.
94 citations
TL;DR: In this paper, three initial vibrational states of H2, ν=0, 1, and 2, were considered in order to study the influence of vibrational reactant energy on the OH production.
Abstract: Classical trajectory calculations of cross sections for the reaction 0(3P)+H2(1Σ+g; ν, j) →OH(2Π; ν′, j′)+H(2S) have been performed for collision energies 1 kcal/mol⩽E⩽40 kcal/mol using an analytical fit to a recent ab inito potential energy surface. Three initial vibrational states of H2, ν=0, 1, and 2, are considered in order to study the influence of vibrational reactant energy on the OH production. With increasing vibrational quantum number, (a) the threshold shifts to lower energies, and (b) the cross sections rise more steeply with collision energy. Rotational excitation of H2 enhances the total reaction cross section for each vibrational state over the range of H2(ν,j) states studied. The cross sections have been used to calculate reaction rate constants for temperatures 300°K⩽T⩽1000°K and the three lowest vibrational states. The ratio k (T,ν=0):k (T,ν=1):k (T,ν=2) is found to be 1:1.13×104:1.42×106 at 300°K and 1:2.12×101:1.24×102 at 1000°K, demonstrating that vibrational energy strongly enhances ...
92 citations
TL;DR: In this paper, a new method for the calculation of the vibrational-rotational energy levels of a triatomic molecule is presented. The method utilizes the well developed techniques of molecular scattering theory and is formulated in a body-fixed reference frame.
Abstract: A new method is presented for the calculation of the vibrational–rotational energy levels of a triatomic molecule. The method provides a means of solving Schodinger’s equation for the bound energy levels of a triatomic system as exactly as desired. The relative motion of the atoms is governed by a potential energy surface, which can be of arbitrary form, but must, naturally, be specified. The method utilizes the well developed techniques of molecular scattering theory and is formulated in a body‐fixed reference frame. The bound state energies appear in the theory as first order poles of a specially constructed T matrix element. Because the analytic behavior of these poles, as a function of the energy, is well defined, the exact bound state energies are easily found. The theory has been applied to the water molecule and results are presented for the lowest five vibrational–rotational energy levels corresponding to zero total angular momentum. These results agree well with previously published values.
65 citations
TL;DR: In this paper, the computation and fitting of an ab initio COH 2 potential energy surface is described and discussed, and the asymptotic forms of the electrostatic, induction and dispersion energies are presented; the dispersion energy calculated at long range yields the values of the parallel and perpendicular components of the quadrupole polarisability tensor, A, of the CO molecule.
60 citations
TL;DR: In this article, a new simple but realistic empirical representation of collinear triatomic potential energy surfaces is proposed and examined, based on the introduction of a novel system of orthogonal coordinates defined in terms of the bond orders of the two bonds.
Abstract: A new simple but realistic empirical representation of collinear triatomic potential energy surfaces is proposed and examined. The approach is based on the introduction of a novel system of orthogonal coordinates defined in terms of the bond orders of the two bonds. The potential surface is represented as an interpolation between the two asymptotic diatomic potentials along these coordinates. In addition to the two diatomic potentials the potential energy surface contains two empirical constants: A coordinate scale factor (which enters into the definition of the bond order via the Pauling relation) and an energy scale factor (which is roughly constant for a series of surfaces with a common central atom).
55 citations
TL;DR: In this paper, an analysis of the saddle point region of the hypersurface provides a structure for the activated complex (rCH=3.35 b, rco=2.15 b, ϑ=115°) and predicts the critical energy (E0=18.5 kcal mol−1).
Abstract: Many‐body perturbation theory (MBPT) and couple‐cluster doubles (CCD) calculation are reported for the formyl radical and for points on the potential energy surface corresponding to decomposition of the radical to hydrogen plus carbon monoxide. The predicted equilibrium structure (rCH=2.1 b, rco=2.245 b, and ϑ=124°) and dissociation energy (De=16.6 kcal mol−1) are in excellent agreement with experimental data. An analysis of the saddle‐point region of the hypersurface provides a structure for the activated complex (rCH=3.35 b, rco=2.15 b, ϑ=115°) and predicts the critical energy (E0=18.5 kcal mol−1). Comparison of MBPT and CCD results for the dissociation energy and barrier height shows that equivalent results are obtained. A RRKM prediction of the decomposition rate coefficient for HCO→H+CO is also given.
53 citations
TL;DR: In this article, the chemiluminescent reaction C2+NO→CN(B 2 ε +CO+2.89 eV has been studied in a crossed molecular beam configuration in a graphite sublimation source operating at 2550°K.
Abstract: The chemiluminescent reaction C2+NO→CN(B 2Σ+) +CO+2.89 eV has been studied in a crossed molecular beam configuration. The carbon beam was obtained from a graphite sublimation source operating at 2550° K. The beam (principally C, C2, C3) was pulsed by a rotating slotted disk before it crossed the NO beam. Electronically excited molecules formed in reaction, CN(B 2Σ+), were detected as they rapidly decayed to the ground state. Photon time‐of‐arrival measurements identified the reactant as C2. The vibrational energy disposal within CN(B 2Σ+) was derived from wavelength resolved measurements. Reaction energetics and the signal intensity indicated the companion product, CO(X1Σ). This study indicates that energy deposition into vibrational degrees of CN(B 2Σ+) disagrees mildly with ’’prior expectation’’ (Levine, Bernstein, and co‐workers). The reaction probably proceeds on a potential energy surface that correlates to C2(X′ 3Πu)+NO(X 2Π).
TL;DR: Quasiclassical trajectory calculations for the H + H 2 reaction with vibrationally excited molecules have been carried out on the Porter-Karplus (PK) and the accurate Siegbahn-Liu-Truhlar-Horowitz (SLTH) potential surfaces as mentioned in this paper.
TL;DR: In deriving the RRS cross section under high pressure, a different approach from that presented in the previous papers has been used, and the resulting expression can be used to treat both pressure and temperature effects.
Abstract: An expression for the resonance Raman scattering (RRS) cross section from large molecules is derived by means of a time independent Green function method. This expression is obtained in the adiabatic basis set, and both the radiative and nonradiative damping effects are explicitly considered, assuming the statistical limit in the excited vibronic states. Expanding the nuclear coordinate dependence of the transition moment, an analytical expression for the RRS cross section is derived for a displaced potential energy surface model. The expression obtained is applicable to the resonance Raman scattering not only in the weak coupling but also in the strong coupling case, and consists of the sum of the nth order vibrational transitions. It is shown that in the weak coupling case, the fundamental cross section may be explained as a succession of the absorption to the lowest level in the excited electronic state followed by the emission from it. Multimode effect on the RRS cross section which has not been repor...
TL;DR: In this article, the real and imaginary parts of the complex potential energy surface of the resonance state and of the transition dipole moment between the ground state of H2 and the resonance states were analyzed.
Abstract: The absorption of photons with an energy of 26.9 eV by H2 produces H+ ions with kinetic energies ranging up to 4.4 eV. We attribute the energetic H+ ions to absorption into a 1Σu+ resonance state of H2 which autoionizes into a continuum corresponding to a free electron moving in the field of the 1sσg core of H2+. We present calculations of the real and imaginary parts of the complex potential energy surface of the resonance state and of the transition dipole moment between the ground state of H2 and the resonance state. The resulting cross section for the production of energetic H+ ions and the calculated ratio of H+ to H2+ ions produced are in agreement with measurements. The energy distribution of the H+ ions has a maximum at about 3.2 eV. The maximum cannot be reproduced by a classical description of the nuclear motion in the autoionizing resonance state, but it does arise when a quantal treatment is used, in which the nuclear motion is governed by the real part of the complex potential.
TL;DR: In this paper, the relative vibration-rotation reaction probabilities for the H + F 2 (ν = 0, j = 0) → HF(ν′, j ′) + F reaction on the best extended LEPS potential energy surface No. II of Jonathan et al. have been computed using a three-dimensional, quantum-dynamical, distorted-wave Born approximation.
TL;DR: In this paper, a new potential energy surface for H3 of the London-Eyring-Polanyi-Sato type has been obtained which reproduces the best available estimates for the geometry, classical barrier height, and quadratic force constants of the D∞h saddle point.
Abstract: A new potential energy surface for H3 of the London–Eyring–Polanyi–Sato type has been obtained which reproduces the best available estimates for the geometry, classical barrier height, and quadratic force constants of the D∞h saddle point. Other attributes of the surface, e.g., minimum energy profile for the exchange process, spherically averaged potential V0, and leading anisotropic potential V2, are also shown to be in good agreement with the best available estimates. The simplicity of its functional form further commends it for future dynamical studies.
TL;DR: Differential and integral cross sections for rotational/vibrational transition in N2 colliding with Li+ have been calculated using a semiclassical collision model as mentioned in this paper, and the potential energy surface used was an analytical 19-parameter fit to 95 ab initio SCF points.
TL;DR: In this paper, an asymmetric rotor molecule in a vibrational state (v 1 v 2 v 2 … vN ) and a rotational states (J τ) is considered, where terms in the expansion up to those quartic in the reduced normal coordinates are taken into account.
Abstract: Molecular properties depend on the state of rotation and vibration. As a result of recent experimental developments such a dependence has been detected by several techniques for a variety of molecular properties of a large number of compounds. By expanding the property P as a power series in the reduced normal coordinates it is possible to derive an expression relating P to the state of rotation and vibration. In the present paper this is done for an asymmetric rotor molecule in a vibrational state (v 1 v 2 … vN ) and a rotational state (J τ). Terms in the expansion of P up to those quartic in the reduced normal coordinates are taken into account. The expression is of the form where Pe (0) is the value of the property at equilibrium, P J τ , Ai J τ and Bij depend on the parameters describing the potential energy surface and the property surface, and a superscript J τ denotes a dependence on rotational state through the quantities ⟨J τ|Πα 2|J τ⟩ where Πα denotes the rotational angular momentum about a prin...
TL;DR: In this paper, the energy dependence of the P T ν′← ν is compared to the LEPS surface for the collinear reaction O( 3 P + H 2 (ν = 0, 1) → OH(ν′) + H using a LEPS and fitted ab initio potential energy surface.
TL;DR: In this paper, the gas phase reaction between F atoms and hydrazoic acid has been studied by arrested relaxation infrared chemiluminescence, and the results suggest that the reaction may proceed via a long-lived HFN 3 intermediate species.
TL;DR: In this article, three-dimensional quasiclassical trajectory calculations for the reaction of Cl atoms with HD were performed for the initial vibrational state v=0, rotational states J=0-4, and collision energies E between threshold and 15.0 kcal/mole.
Abstract: Results of three‐dimensional quasiclassical trajectory calculations for the reaction of Cl atoms with HD are reported. Calculations were performed for the initial vibrational state v=0, rotational states J=0–4, and collision energies E between threshold and 15.0 kcal/mole. Reaction probabilities, cross sections, thermal rate constants, product energy partitioning, and product angular distributions, for the two competing branches Cl+HD→HCl+D and Cl+DH →DCl+H, are presented and discussed. The kinetic isotope effects kCl+HD/kCl+DH, kCl+H2/(kCl+HD +kCl+DH), and kCl+H 2/kCl+D2 obtained from this study and from earlier trajectory calculations are compared with experimental data and with results of TST and classical 1D trajectory calculations, using the same potential energy surface.
TL;DR: In this article, a realistic potential energy surface has been used, and the vibrational transition rates are averaged over rotational-translation distributions at 4500°K, where the same transition rates were calculated by eight distorted wave-based theories which have been used by others for various applications.
Abstract: Quasiclassical trajectory calculations of vibrational transition rates in Ar+H2 collisions have been carried out. A realistic potential energy surface has been used, and the rates are averaged over rotational–translation distributions at 4500 °K. The same transition rates are calculated by eight distorted‐wave‐based theories which have been used by others for various applications. The present calculations provide a critical test of these theories, especially for high vibrational quantum numbers where data has been scarce. We also discuss dissociation rates, the rotational component of vibrational energy transfer, and a surprisal analysis of the vibrational transition rates.
TL;DR: In this paper, molecular orbital calculations have been carried out on various structures of LiAlF 4 complex using minimal and extended basis sets and a C 2v structure with two fluorines in the bridge was found to be more stable than structures with one and three fluorines.
TL;DR: In this paper, the authors used the quasiclassical trajectory method and a realistic potential energy surface to calculate rate constants and Arrhenius activation energies for dissociation of p • H2 in Ar from each of H2′s fifteen different vibrational levels at a rotational-vibrational temperature of 4500°K.
Abstract: We have used the quasiclassical trajectory method and a realistic potential energy surface to calculate rate constants and Arrhenius activation energies for dissociation of p‐H2 in Ar from each of H2′s fifteen different vibrational levels at a rotational–vibrational temperature of 4500°K We have also calculated the equilibrium rate constant and energy of activation and many other attributes of the equilibrium reaction at 4500°K The effect of considering the seven quasibound states with longest unimolecular lifetimes as reactant states is also studied in detail Reaction is favored by high internal energy—either high rotational quantum number at low vibrational quantum number or vice versa In particular, at equilibrium the groups of vibrational levels with vibrational quantum numbers v equal to 0–6, 7–11, and 12–14 contribute 26%, 48%, and 26% to the reaction rate Dissociation from low v levels proceeds primarily from the topmost j state for a given v level; as a consequence neither the assumption of vibrational equilibrium nor the assumption of rotational equilibrium is valid for treating nonequilibrium effects
TL;DR: In this article, the essential features (geometries of the minima and of the saddle points, energy barriers) of the potential energy surface of the four hydrides YXH4 mentioned in the title have been determined with two basis sets, of minimal and DZ quality respectively.
Abstract: The essential features (geometries of the minima and of the saddle points, energy barriers) of the potential energy surface of the four hydrides YXH4 mentioned in the title have been determined with two basis sets, of minimal and DZ quality respectively. The importance of the different extent of the deformation of the XH4 group in the different structures of the four hydrides is brought out and discussed. The aspects of charge distribution and bonding are examined drawing on population analysis, comparison of the electrostatic molecular potentials and decomposition of the interaction energy (this last referred to the Y+ + XH
4
−
→ YXH4 process). The capability of XH3 in effecting the etherolytic disruption of the Y-H bond is finally brought out.
TL;DR: The semi-empirical molecular orbital method MINDO/3 was used to investigate the potential energy surface for the H 2 and H 2 O elimination reactions of protonated methanol as discussed by the authors.
TL;DR: In this paper, the authors studied the dissociation of CO2 ions formed by electron attachment with a classical trajectory method in which the initial conditions are represented by the Wigner probability density function and the electronic state 2Σ+g of CO−2 is described by a Wall-Porter potential energy surface.
Abstract: The dissociation of the 2Σ+g CO−2 ions formed by electron attachment is studied with a classical trajectory method in which the initial conditions are represented by the Wigner probability density function and the electronic state 2Σ+g of CO−2 is described by a Wall–Porter potential energy surface. Since both the ground initial state of CO2 and the upper dissociative state of CO−2 have an equilibrium angle of 180°, the dissociation is studied through the collinear approximation. The experimental data (excess energy transferred to vibration, population inversion of the vibrational CO levels) are found to be related not only to the autodetachment rate as usual, but also to some details of the repulsive potential energy surface such as the position and height of the saddlepoint and to the inertial coupling between translation and vibration.
TL;DR: In this paper, the initial results of an exact treatment of a simplistic model for solvent effects on cation-anion combinations are presented, which consists of two charges and eight finite dipoles interacting through coulombic forces and [1/r]**12 repulsions.
Abstract: Some general concepts involved in theories of solvent effects on ionic reactions in solution are discussed and some fallacies in extant theories are pointed out. The initial results of an exact treatment of a simplistic model for solvent effects on cation-anion combinations are presented. The model system consists of two charges and eight finite dipoles interacting through coulombic forces and [1/r]**12 repulsions. Local minima in the potential energy surface of the system are found which correspond to “solvent-separated” ion pairs and “intimate” ion pairs, and reaction paths and saddle points connecting the species have been found.
TL;DR: In this article, a generalized diatomics-in-molecules (GDIM) method within the framework of semi-empirical valence bond theory is proposed as a means for fitting potential energy surfaces.
Abstract: The diatomics-in-molecules hamiltonian has been cast into the most general form composed of fragment hamiltonians, interatomic interaction potential energy terms and arbitrary functions of molecular geometry with adjustable parameters. Based on this hamiltonian, a generalized diatomics-in-molecules (GDIM) method within the framework of semiempirical valence bond theory is proposed as a means for fitting potential energy surfaces. The method requires evaluation of interactomic interaction energies in terms of molecular integrals and utilizes the geometry functions as a calibration device. A preliminary application to the H3 system is reported. With only one fitting parameter in the entire treatment, the GDIM potential energy surface has a classical barrier height in agreement with the most accurate ab initio CI value and, for linear symmetric points in the significant range of H-H distances, it has a root-mean-square deviation of 0·0012 hartree from the most accurate ab initio energies. An extension of the...
TL;DR: In this paper, the potential energy surface for the insertion of singlet methylene into H2 has been computed on the ab initio SCF level as well as with inclusion of electron correlation by means of the CEPA method.
Abstract: The potential energy surface for the insertion of singlet methylene into H2 has been computed on theab initio SCF level as well as with inclusion of electron correlation by means of the CEPA method. The results are compared with those of previous semiempirical,ab initio SCF and CI calculations. The system is a prototype of a reaction where an allowed and a symmetry-forbidden path can compete. The electron correlation energy was found to be very different for different regions of the surface, but did not have much influence on the optimum reaction path. From the computed heat of the reaction, the heat of formation of singlet methylene was estimated to be 101.5 kcal/mol. According to the calculations the reaction does not need any activation energy.