Further studies of the methyl nitrite cis→trans isomerization

Abstract

Classical trajectory calculations have been performed to get more insights into the dynamics of cis→trans isomerization of methyl nitrite. Harmonic (diagonal and nondiagonal) and anharmonic potential energy surfaces with parameter values based on the available experimental data and our own ab initio results have been used in these computations. The ab initio calculations have been carried out at the MP2 and QCISD levels of theory, employing the 6-311++G** basis set. Coupling of vibrational modes is analyzed in detail. The influence of molecular rotation and isotopic substitution on the isomerization rate is investigated. Mode specific effects are clearly exhibited for the diagonal-harmonic potential, but they are significantly reduced by inclusion of anharmonicity or interaction terms in the potential function. It is found that modes that exhibit specificity are coupled with the reaction coordinate and with other vibrational modes that couple with the reaction coordinate as well. A comparison of rate coefficients computed for several deuterated species show an unexpected secondary isotope effect.