Ab initio study of the HNC → HCN isomerization. II. Calculation of the isomerization rate constant

Abstract

The rate constant for the HNC → HCN isomerization is calculated employing two variants of the RRKM method. The first set of results is obtained according to the traditional RRKM model whereby the state densities and the partition functions are determined by direct counting of energy levels calculated in the harmonic-oscillator-rigid-rotor approximation, treating HNC and the activated complex as two distinct species. The second series of calculations is based on a previous determination of vibration-rotation energy levels corresponding to the entire potential-energy surface. The transition from HNC into HCN is treated as a consequence of highly excited bending vibrations followed by fast redistribution of the energy. The formula for the unimolecular rate constant is correspondingly modified. © 1984.