Showing papers on "Potential energy surface published in 1982"
TL;DR: A formalism for the application of variational transition state theory and semiclassical vibrationally adiabatic transmission coefficients to bimolecular reactions involving an arbitrary number of atoms is presented in this paper.
Abstract: A formalism for the application of variational transition‐state theory and semiclassical vibrationally adiabatic transmission coefficients to bimolecular reactions involving an arbitrary number of atoms is presented. This generalizes previous work on atom–diatom reactions. We make applications in this paper to the reactions OH+H2→H2O+H and OH+D2→HDO+D using the Schatz–Elgersma fit to the Walch–Dunning ab initio potential energy surface. For both reactions we find large differences between conventional and variational transition‐state theory and large effects of anharmonicity on the calculated rate constants. The effect of reaction‐path curvature on the calculated transmission coefficients and rate constants is also large. The final calculated values of the kinetic isotope effects are in good agreement with experiment at high temperature but too large at room temperature.
256 citations
TL;DR: In this article, the potential energy surface of the LiH molecule was calculated using the Green's function Monte Carlo method and the calculated correlation energy is 0.078±0.001 hartree and the binding energy is 2.56 eV.
Abstract: The potential energy surface of the LiH molecule is calculated using the Green’s function Monte Carlo method. The calculated correlation energy is 0.078±0.001 hartree and the binding energy is 2.56 eV. These results are within 6% and 2% of the experimental values, respectively. The Green’s function Monte Carlo method is discussed in some detail with particular emphasis on problems of chemical interest.
165 citations
132 citations
TL;DR: In this paper, a variational method is presented for the determination of vibrational frequencies which is suitable for any triatomic molecule and is expressed as a function of two bond lengths and the included angle.
Abstract: Assuming that the potential energy surface is known, a variational method is presented for the determination of vibrational frequencies which is suitable for any triatomic molecule The harniltonian is expressed as a function of two bond lengths and the included angle The expansion functions are products of either Morse oscillator functions or harmonic oscillator functions for the stretching vibrations and spherical harmonics for the bending vibration Results are presented for linear, quasilinear and bent molecules
125 citations
TL;DR: In this article, an analytic fit to the two-dimensional surface (the CN bond length is frozen at 2.186 a 0 ) is presented, using a large polarised GTO basis.
106 citations
TL;DR: In this article, the state-selected reaction rates were calculated by an extension of variational transiton state theory, where the reactant vibrational modes were assumed to correlate diabatically with generalized normal modes of a generalized activated complex.
Abstract: The state‐selected reaction rates OH(nOH = 0,1)+ H2(nHH = 0,1)→H2O+H are calculated by an extension of variational transiton state theory. The reactant vibrational modes are assumed to correlate diabatically with generalized normal modes of a generalized activated complex. Using the Walch‐Dunning‐Schatz‐Elgersma ab initio potential energy surface, the theory predicts that excitation of H2 is 19–68 times more effective than excitation of OH in promoting reaction at 300 K, where the range of values corresponds to different possible assumptions about the quantal effects on reaction‐coordinate motion. These values are in much better agreement with the experimental value (about 100) than is a calculation based on the conventional transition state, which yields 2×104.
105 citations
TL;DR: The IHI system has four vibrationally bonded collinear bound states, which are located in the saddle point region of a minimum-free potential energy surface as mentioned in this paper, which is the same region of the IHI saddle point.
87 citations
TL;DR: In this paper, the ICVT/MCPSAG theory and LSTH surface were employed to predict the rate coefficients for all three reactions in three dimensions. But they were not tested for sensitivity to variations in the potential energy surface by repeating the calculations for the less accurate Porter-Karplus surface.
Abstract: We consider three reactions: H+H2→H2+H; Mu+H2→MuH+H; Mu+D2 →MuD+D. We calculate accurate quantum mechanical reaction probabilities and thermal rate coefficients for all three reactions in collinear geometry using the Liu–Siegbahn–Truhlar–Horowitz (LSTH) accurate potential energy surface. These rate coefficients are used to test conventional transition state theory and the improved canonical variational theory with Marcus–Coltrin‐path semiclassical adiabatic ground‐state transmission coefficients (ICVT/MCPSAG). The ICVT/MCPSAG theory is found to be greatly superior and reasonably reliable. These conclusions are tested for sensitivity to variations in the potential energy surface by repeating the calculations for the less accurate Porter–Karplus surface. The conclusions are unaltered by this. The ICVT/MCPSAG theory and LSTH surface are then employed to predict the rate coefficients for all three reactions in three dimensions.
70 citations
TL;DR: In this paper, the effects of electron correlation on the calculated properties of the (HOHOH)− anion were studied using Mo/ller-Plesset perturbation theory.
Abstract: The effects of electron correlation on the calculated properties of the (HOHOH)− anion are studied using Mo/ller–Plesset (MP) perturbation theory. With this technique, inclusion of corrections up to third order are shown to provide results quite similar to those obtained with an extensive CI approach when equivalent basis sets are used. Barriers to proton transfer between the two oxygen atoms at a fixed R(OO) distance are computed with a number of basis sets ranging from split‐valence 4–31G to triple‐valence with polarization functions on all atoms, 6–311G**. Each successive enlargement of the basis set leads to a greater barrier. The second‐order correction to the energy reduces the Hartree–Fock barrier dramatically while subsequent inclusion of the third‐order energy results in an increase over the MP2 barriers. MP3 formalism is found capable of accurately reproducing CI results for both the barrier height and functional dependence of the correlation energy upon the proton position. The potential energy surface is calculated as a function of both the R(OO) distance and the position of the central proton. At the Hartree–Fock level, all basis sets yield a surface with two minima separated by a saddle point, representing the transition state for adiabatic proton transfer. The surface is flattened a great deal by inclusion of second‐ and third‐order corrections such that the barrier to proton transfer is considerably below the estimated zero vibrational level for protonic motion. Electron correlation effects are also responsible for an increase of about 3 kcal/mol in the hydrogen‐bond energy of the (HOHOH)− complex.
67 citations
TL;DR: In this paper, an extended polarized basis set and Moller-Plesset perturbation theory including triple substitution correlation corrections in the fourth-order treatment indicate that singlet ethylidene (CH3CH:) is not a local minimum on the C2H4 potential energy surface.
65 citations
TL;DR: In this paper, a diabatic formalism for the treatment of chemical reactions is introduced, using hyperspherical coordinates and expansions for both potentials and wavefunctions in H 3.
TL;DR: In this paper, a quasiclassical trajectory study of the thermoneutral isotopic oxygen exchange reaction was made using a recently reported potential energy surface for the ground state of ozone.
TL;DR: In this paper, the Fourier transform of an optical electronic spectrum leads to an autocorrelation function C(t) which describes the evolution in time of the wave packet created by the Franck-Condon transition, as it propagates on the potential energy surface of the electronic upper state.
Abstract: The Fourier transform of an optical electronic spectrum leads to an autocorrelation function C(t) which describes the evolution in time of the wave packet created by the Franck–Condon transition, as it propagates on the potential energy surface of the electronic upper state. This correlation function is equal to the modulus of the overlap integral between the initial position of the wave packet and its instantaneous position at time. The original data resulting from an experimentally determined spectral profile must be corrected for finite energy resolution, rotational, and spin‐orbit effects. The behavior of the system can then be followed up to a time of the order of 10−13 s, i.e., during the first few vibrations which follow immediately the electronic transition. The method is applied to photoelectron spectra and the results are compared to the available information on potential energy surfaces of ionized molecules, in order to study their unimolecular dissociation dynamics. In the case of the X 2Σ+g, ...
TL;DR: The first ab initio determination of the rate constants for the reaction of ethynyl radical C2H with molecular hydrogen is presented in this article, where the potential energy surface was determined in the seagent and saddle point regions using configuration interaction methods and the rate constant was evaluated using transition state theory.
Abstract: The first ab initio determination of the rate constants for the reaction of ethynyl radical C2H with molecular hydrogen is presented. The potential energy surface was determined in the seagent and Saddle point regions using configuration interaction methods and the rate constant was evaluated using transition state theory. (AIP)
TL;DR: In this paper, a three-dimensional quasiclassical trajectory study of the Li→HF→LiF+H reaction has been performed on a recently proposed analytical potential energy surface (PES) fitted to ab initio points.
Abstract: A three‐dimensional quasiclassical trajectory study of the Li→HF→LiF+H reaction has been performed on a recently proposed analytical potential energy surface (PES) fitted to ab initio points. The results of the calculations are compared with the experiment. Previous related work on a semiempirical PES is noted.
TL;DR: In this article, an analytical potential energy surface is determined, from which the barrier to linearity is calculated to be 931 cm −1 (α e = 137°), demonstrating how reliable J = 0 and J = 1 vibrational levels can be calculated variationally for such a quasi-linear molecule with a small barrier height.
TL;DR: In this paper, the authors measured the total reaction cross section as a function of initial translational energy by using a He/Ne buffer gas mixture to vary the O atom velocity, and the threshold energy E 0 = 14 ± 2 kJ mol-1 for the formation of HSO product was in good agreement with the activation energy for the overall reaction of O atoms with H2S molecules.
Abstract: Reactive scattering of O atoms with H2S molecules has been studied at an initial translational energy E≅30 kJ mol-1 using a supersonic beam of O atoms seeded in He. Reactive scattering of HSO radicals is nearly isotropic but slightly favours the backward hemisphere with a product translational energy E′av∼26 kJ mol-1. The total reaction cross section was measured as a function of initial translational energy by using a He/Ne buffer gas mixture to vary the O atom velocity. The threshold energy E 0 = 14 ± 2 kJ mol-1 for the formation of HSO product is in good agreement with the activation energy for the overall reaction of O atoms with H2S molecules. Hence the formation of HSO product represents an important primary pathway for the O + H2S reaction which is initiated by bonding of the electrophilic O atom to the lone pair electrons of the S atom. The potential energy surface for H atom displacement has a barrier in the exit valley which promotes nearly isotropic scattering and high product translational ene...
01 Jan 1982
TL;DR: In this article, the relative integral cross section of the two endothermic reactions K + HCl(υ = 0 and 1) → KCl + H and K + HF(π = 0, 1)→ KF + H has been measured as a function of the collision energy E using the crossed molecular beam technique.
Abstract: The relative integral cross section for the two endothermic reactions K + HCl(υ = 0 and 1) → KCl + H and K + HF(υ = 0 and 1) → KF + H has been measured as a function of the collision energy E using the crossed molecular beam technique. The vibrationally excited state (υ = 1) has been populated thermally by heating the beam source to temperatures around 2000 K. The variation of the collision energy from thermal up to around 2.1 eV was achieved by seeding the K-beam with various carrier gases. The molecular reaction product was detected by surface ionization in connection with a time-of-flight method. The total energy threshold of the reactions has been found to be equal to or only slightly above the corresponding endothermicities. This suggests a vanishing or very low barrier crest on the potential energy hypersurfaces which is contradictory to recent theoretical results. The inclusion of tunneling in case of K + HF leads to a negligible rise of the barrier heights. The efficacy of translational and vibrational energy in promoting the reactive process has been directly compared over a wide range of collision energies. For K + HCl the vibrational enhancement of the reactivity descends with increasing E from approximately a factor of 10 at E = 0.08 eV to around unity for E ⩾ 0.5 eV. The good agreement of this experimental result with phase space calculations suggests that the marked enhancements are predominantly caused by the long-range attraction between reagents in connection with an “early” barrier on the potential energy surface. In case of K + HF vibrational energy is by a factor of up to 380 more favourable in promoting the reaction than the same amount of translational energy. Again, with rising collision energy its efficacy decreases but promotes the reaction still by a factor of 70 at E = 1.7 eV. Since phase space theory fails here the reaction is certainly non-statistical and we conclude that the observed large efficacy of vibrational energy is due to a “late” barrier. The proposed barrier positions for the two systems are in accordance with theoretical results.
TL;DR: In this paper, a double-zeta quality basis set augmented with polarization and diffuse functions has been used to characterize low-lying potential energy surfaces of the methoxy radical at C3v conformations using ab initio quantum chemical techniques.
Abstract: Several low‐lying potential energy surfaces of the methoxy radical have been studied at C3v conformations using ab initio quantum chemical techniques. A double‐zeta quality basis set augmented with polarization and diffuse functions has been used throughout. Eight doublet and quartet states have been characterized as a function of C–O distance. The equilibrium conformation of the 2E ground state is found (RCO = 1.405 A, RCH = 1.112 A, ϑHCO = 111.3°), and the harmonic vibrational frequencies of the three a1 modes are calculated (3118, 1330, and 1017 cm−1). The ? 2A1←? 2E vertical excitation energy has been estimated to be 4.01 eV. The wave functions for the ? and ? states have been analyzed in terms of their dipole moments, population analyses, and orbital contour plots.
TL;DR: In this paper, electron correlation using third-order perturbation theory leads to a substantial relative destabilization of the isocyanide form for both NaCN and KCN, and improves agreement between observed and theoretical geometries for KCN.
Abstract: Ab initio molecular orbital calculations using large Gaussian basis sets have been performed for NaCN and KCN with full geometry optimization. Potential energy surface obtained are sensitive to the quality of polarization functions used on C and N. A bent structure, as found experimentally for KCN, is the lowest energy geometry for both NaCN and KCN, with the isocyanide form only 5–6 kJ mol−1 higher at the SCF level. Inclusion of electron correlation using third‐order perturbation theory leads to a substantial relative destabilization of the isocyanide form for the both NaCN and KCN, and improves agreement between observed and theoretical geometries for KCN.
TL;DR: In this article, the rotational rainbow structures in differential cross sections for the prototypical Ne-Na2 system were investigated using an accurate CI potential energy surface, which includes electron correlation effects for the bond orbital of Na2 and the L • shell orbitals of Ne together with the dispersion attraction between the two subsystems using the method of self-consistent electron pairs.
Abstract: A thorough investigation of rotational rainbow structures in differential cross sections for the prototypical Ne–Na2 system is presented. The scattering calculations are performed using an accurate CI potential energy surface, which includes electron correlation effects for the bond orbital of Na2 and the L‐shell orbitals of Ne together with the dispersion attraction between the two subsystems using the method of self‐consistent electron pairs (SCEP). The surface is dominantly repulsive and highly anisotropic. A very shallow van der Waals minimum of about 0.3 meV is obtained at large internuclear distances. Coupled states and infinite‐order‐sudden differential cross sections are compared for a wide range of collision energies which allows for a critical test of the energy‐sudden condition. The applicability of the centrifugal sudden approximation for Ne–Na2 is also discussed. In particular, we investigate the dependence of the rotational rainbow structures on collision energy and initial rotational state. The positions of the primary rotational rainbows obtained with the CI and the corresponding Hartree–Fock surface are compared to experimental results. We find satisfactory agreement for the CI surface but considerable deviations if the Hartree–Fock surface is used. Finally, we compare the scattering results for Ne–Na2 with those for He–Na2 and conclude that at low energies (E≲100 meV) the drastic differences are mainly due to the different masses rather than the potential energy surfaces.
TL;DR: In this paper, the γ-vibrations in 168 Er were analyzed in a macroscopic and in a microscopic model with special emphasis on the anharmonicities of two-phonon states.
TL;DR: In this paper, the dependence of final vibrational energy, final phase, and trajectory time on the initial phase of the H2 reagent was examined on a novel potential energy surface for the collinear H3 system.
Abstract: The dependence of final vibrational energy, final phase, and trajectory time on the initial phase of the H2 reagent is examined on a novel potential energy surface for the collinear H3 system. For the first time, the fine structure in the borders of the reactivity bands is reported in some detail. A complex, exponentially crowding structure is found in contrast to the common impression of ’’chaotic’’ behavior in these regions. The close relation of this structure to the concepts of periodic and exponentiating trajectories is discussed. A suggestion for the implications to Feshbach resonances in semiclassical theory is made.
TL;DR: Vibrational threshold equal to the barrier height for an endothermic reaction: Li+FH→LiF+H on an ab initio potential energy surface is considered in this article.
Abstract: Vibrational threshold equal to the barrier height for an endothermic reaction: Li+FH→LiF+H on an ab initio potential energy surface is considered. (AIP)
TL;DR: In this paper, a vibrationally adiabatic model is used to predict the positions of resonances in reactive scattering for collinear H + H/sub 2/, H + FH, and isotopic analogues of these reactions.
Abstract: A vibrationally adiabatic model is used to predict the positions of resonances in reactive scattering for collinear H + H/sub 2/, H + FH, and Cl + H/sub 2/ and isotopic analogues of these reactions and for three-dimensional H + H/sub 2/. Good agreement was obtained with accurate quantum mechanical results for both shape and Feshbach resonances. In some cases the agreement is better if it is assumed that the system follows a dynamical path on which the internal centrifugal forces are balanced by the potential energy surface than if it is assumed that the system follows the minimum-energy path.
TL;DR: In this paper, an approximate variational solution of the vibrational Eckart hamiltonian is presented for several states of the rotational spectrum of a potential energy surface for the KCN.
Abstract: Dynamical calculations are performed on an ab initio potential energy surface for KCN. Approximate variational solutions of the vibrational Eckart hamiltonian are presented for several states. Fundamental vibrations are found to lie at 302·7 cm-1 and 119·7 cm-1. An effective rotational hamiltonian is solved for several vibrational states allowing vibrational assignments to be made to the observed rotational spectrum.
TL;DR: In this paper, total and state-to-state quantum-mechanical collinear reactive probabilities for the title reactions have been computed on a recently proposed potential energy surface and compared with previous work.
TL;DR: In this article, the mid-infrared and Raman combination and hot band spectra involving the ring puckering (ν22), ring deformation (ν6), and SiH2 in-phase rocking (ν21) vibrations have been analyzed for 1,3disilacyclobutane in order to determine the ringpuckering energy levels for the ground and excited state of the other two vibrations.
Abstract: The mid‐infrared and Raman combination and hot band spectra involving the ring‐puckering (ν22), ring‐deformation (ν6), and SiH2 in‐phase rocking (ν21) vibrations have been analyzed for 1,3‐disilacyclobutane in order to determine the ring‐puckering energy levels for the ground and excited state of the other two vibrations. The puckering levels are only slightly perturbed in the rocking excited state but substantially altered in the ring‐deformation excited state. The parameters of the three‐dimensional potential energy function V = a1x41+b1x21+b2x22+ b3x23+c12x21x22+c13x21x2 3, where the subscripts 1, 2, and 3 refer to ν22, ν6, and ν21, respectively, were adjusted in order to obtain the best fit between the observed and calculated frequencies. For the energy level calculations, the Hamiltonian was symmetry factored into eight separate symmetry blocks. The basis functions for the three‐dimensional calculation were determined by first solving the one‐dimensional problem in x1 and multiplying the resulting ei...