Mode Specificity and the Influence of Rotation in CIS-Trans Isomerization and Dissociation in HONO.

摘要

The results of a classical trajectory study of intramolecular vibrational energy redistribution, cis-trans isomerization, and unimolecular dissociation in Nitrous Acid are presented. The calculations were carried out on a realistic potential-energy surface that was constructed by using the available kinetic, thermochemical, spectroscopic, and ab initio quantum mechanical information. The influence of the total energy, initial normal-mode excitations, initial OH-stretch overtone excitations, rotation, and potential-energy surface on intramolecular vibrational redistribution and the initial rates of isomerization and dissociation is discussed. The results show significant mode-specific behavior, particularly for the isomerization. Excitations of overtones of the OH or N=O bond stretching modes yield the lowest initial rates for both isomerization and dissociation. Excitation of the HON bending mode yields the largest isomerization rates while excitation of the ONO bending mode yields the largest dissociation rate. At a fixed total energy, placing a small amount of rotational energy in the molecule causes a significant increase in the isomerization and dissociation initial rates over those computed for nonrotating HONO, however, when the rotational energy is increased above 0.1 eV, the rates decrease as expected on the basis of RRKM theory. The orientation of the rotation is an important factor for the intramolecular energy transfer and reaction rates. Reprints. (aw)