Resonances and fluctuations in the unimolecular reaction of NO2

Abstract

Fluctuations and oscillations in the unimolecular reaction of NO₂, and their manifestations in photofragment yield (PHOFRY) spectra, NO rotational state distributions and decomposition rates are examined. Comparisons between experimental and simulated PHOFRY spectra show that extraction of rates from linewidths in state-selected spectra is unjustified in the regime of overlapping resonances. Measurements of the alignment parameter of the NO product in the excess energy range E^E= 200–500 cm^–1 evidence the existence of fluctuations in the decay rate. Changes in the patterns of fluctuations and oscillations in the NO rotational state distributions reveal the progressive tightening of the transition state (TS) as the excess energy increases and the importance of exit-channel interactions beyond the TS. Distributions well fit on the average by phase-space calculations can be obtained even when the transition state is tight.