Journal ArticleDOI
The anharmonic force field and equilibrium structure of methane
D.L. Gray,A.G. Robiette +1 more
TLDR
In this article, the anharmonic force field of methane has been refined to fit spectroscopic data from the isotopic species 12CH4, 13 CH4, 12 CH4.Abstract:
The anharmonic force field of methane has been refined to fit spectroscopic data from the isotopic species 12CH4, 13CH4, 12CH4, 12CH3D, 12CHD3 and 12CH2D2. Six of the thirteen cubic force constants have been determined experimentally, the remaining cubic constants being fixed at values derived from ab initio calculations. The quartic force field is very crude, in that only frrrr has been refined. It is concluded however that the cubic and quartic force fields, even though they are subject to limitations, provide a considerable improvement in the experimental determination of the r e structure and the quadratic force field. The equilibrium bond length is found to be r e(CH) = 1·0858 ± 0·001 A.read more
Citations
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New scale factors for harmonic vibrational frequencies using the B3LYP density functional method with the triple-xi basis set 6-311+G(d,p)
Martin Andersson,Per Uvdal +1 more
TL;DR: The 6-311+G(d,p) basis set is found to give almost converged frequencies for most molecules, and it is concluded that the optimum frequency scaling factors are valid for the basis sets 6- 311G( d, p) to6-311++G(3df,3pd).
Journal ArticleDOI
Frequency and zero-point vibrational energy scale factors for double-hybrid density functionals (and other selected methods): can anharmonic force fields be avoided?
TL;DR: Uniform frequency scaling factors for true anharmonic fundamentals and ZPVEs obtained from quartic force fields are obtained and simple uniform scaling is clearly inadequate.
Journal ArticleDOI
On the relationship of normal modes to local modes in molecular vibrations
TL;DR: In this article, a simple model for the effective vibrational hamiltonian of the XH stretching vibrations in H2O, NH3 and CH4 is considered, based on a morse potential function for the bond stretches plus potential and kinetic energy coupling between pairs of bond oscillators.
Journal ArticleDOI
Dynamics of the activated dissociative chemisorption of CH4 and implication for the pressure gap in catalysis: A molecular beam–high resolution electron energy loss study
M. B. Lee,Q. Y. Yang,S. T. Ceyer +2 more
TL;DR: In this article, the dynamics of activated dissociative chemisorption of CH4 on Ni(111) were studied by molecular beam techniques coupled with high-resolution electron energy loss spectroscopy.
Journal ArticleDOI
The anharmonic force field of ethylene, C2H4, by means of accurate ab initio calculations
TL;DR: In this paper, the quartic force field of ethylene, C2H4, has been calculated ab initio using augmented coupled cluster, CCSD(T), methods and correlation consistent basis sets of spdf quality.
References
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Journal ArticleDOI
PNO–CI Studies of electron correlation effects. I. Configuration expansion by means of nonorthogonal orbitals, and application to the ground state and ionized states of methane
TL;DR: In this paper, the convergence of the configuration expansion of a many-electron wave function was improved without significantly complicating the energy matrix elements by using partially non-orthogonal orbitals.
Journal ArticleDOI
Anharmonic force constant calculations
A.R. Hoy,Ian Mills,G. Strey +2 more
TL;DR: The relationship of the anharmonic force constants in curvilinear internal coordinates to the observed vibration-rotation spectrum of a molecule is reviewed in this paper, where a simplified method of setting up the required non-linear coordinate transformations is described: this makes use of an L tensor, which is a straightforward generalization of the L matrix used in the customary description of harmonic force constant calculations.
Journal ArticleDOI
The vibration-rotation energies of tetrahedral XY4 molecules : Part I. Theory of spherical top molecules
TL;DR: In this paper, the theory of vibration-rotational perturbations in tetrahedral XY 4 molecules has been reexamined in the light of the modern theory of angular momentum coupling, and it is shown that, even to third order of approximation, the splitting of a vibration rotation level into its tetralinear sublevels is governed only by perturbation terms of one basic symmetry in all states in which vibrational quanta of ν 1, ν 3, and ν 4 are excited and to a certain approximation in many of the infrared active states in
Journal ArticleDOI
The calculation of force constants and normal coordinates—IV XH4 and XH3 molecules
J.L. Duncan,Ian Mills +1 more
TL;DR: In this paper, normal coordinate calculations of XH 4 and XH 3 molecules are reviewed and discussed, and it is shown that for most of these molecules the true values of the force constants in the most General Harmonic Force Field can be uniquely determined only by making use of vibration-rotation interaction constants.