Gaussian binning of the vibrational distributions for the Cl + CH _4(v _(4/2) = 0, 1) → H + CH _3Cl(n _1n _2n _3n _4n _5n _6) reactions

摘要

We test several binning techniques to obtain mode-specific final-state distributions for polyatomic reactions. Normal mode analysis is done after an exact transformation to the Eckart frame. Standard histogram binning (HB) and three different variants of the energy-based Gaussian binning (1GB) are employed to obtain the probabilities of the vibrational states. We consider the two major issues of the polyatomic quasiclassical product analysis, i.e., (1) rounding the classical action to the nearest integer can result in unphysical states and (2) the normal-mode analysis can break down for highly distorted geometries. We show that 1GB can handle issue 1 when the total vibrational energy is evaluated in the normal mode space using the harmonic approximation and both issues 1 and 2 can be solved when the total vibrational energy is calculated exactly in the Cartesian space. We found that anharmonicity in the quantized energy levels does not have a significant effect on the final-state distributions. Quasiclassical trajectory calculations are performed for the reactant ground-state and bending-excited Cl(~2P _(3/2)) + CH _4(v _(4/2) = 0, 1) → H + CH _3Cl reactions using an ab initio potential energy surface. The product analysis techniques are successfully applied to the CH _3Cl product molecules and some qualitative features of the results are discussed.