Internal state distributions of CO from HNCO photodissociation

摘要

The internal state distributions of CO produced by photodissociation of HNCO at 1930 (230.1 nm) and at 10thinsp;200 cmminus;1(193.3 nm) in excess of the dissociation energy are determined from multiphoton ionization spectra of the CO fragment measured under collisionhyphen;free conditions. The rotational state distribution of the CO produced at the lower photolysis energy is characterized by a temperature of (491plusmn;23) K. The rotational state distribution of CO produced by photodissociation at the higher photon energy in not well characterized by a temperature. This latter distribution has maximum population nearJ=37, extends beyondJ=65, and accounts for sim;20percnt; of the available energy in excess of that necessary to rupture the HNndash;CO bond. An impulsive dissociation model assuming that dissociation occurs from an excited HNCO complex containing a nonlinear Nndash;Cndash;O configuration accounts for the average CO rotational excitation while phasehyphen;space theory does not agree with the observed distributions. Fitting a semiclassical model to the data using a logically constructed potential energy surface and a groundhyphen;statehyphen;dependent function provides a useful parametrization for the impulsive dissociation. Although not absolute, this analysis suggests that the dissociation occurs directly on a repulsive excited state potential energy surface.