ROTATIONAL EFFECTS ON THE OVERTONE-INDUCED ISOMERIZATION RATE FOR CHD2NC-]CHD2CN

CHD2NC reactant was prepared in a few rotational states, with approximately 1.7 kcal/mol of excess vibrational energy above the barrier to isomerization, by excitation of well-resolved (DELTA-K)Q bandheads of the 5-0 C-H overtone spectrum. Experiments were performed in a static gas cell using IR absorption to monitor the progress of the reaction and a Stern-Volmer analysis to determine the rate constants. The isomerization rate constants were found to decrease significantly as the K quantum number of the excited reactants increased. Rice-Ramsperger-Kassel-Marcus calculations including angular momentum effects have been used in an attempt to simulate the observed isomerization rate constants over the small energy range of this study. Calculations using either conservation or nonconservation of the K quantum number cannot qualitatively reproduce the observed decrease in rate constant with increasing K. We are unable to establish the origin of this discrepancy.