State-selective photochemistry: the predissociation dynamics of jet-cooled dichlorofluoronitrosomethane (CCl2FNO) in the 600 nm region

Abstract

The predissociation dynamics of the substituted nitrosomethane CCl₂FNO (dichlorofluoronitrosomethane) in the 660 nm region have been studied using jet-cooling, state-selective excitation by a pulsed dye laser and delayed LIF probing of nascent NO(X). Energy disposal into NO and the shapes of its rotational state distributions are relatively insensitive to the selected parent molecular vibronic state but mimic statistical (prior) distributions, providing little evidence for state-specific effects. In contrast, photofragment yield spectra and fluorescence decay profiles of the parent molecule indicate that skeletal rocking and bending modes in combination with the torsion (a″ symmetry) act as promoting modes for the radiationless transition, resulting in the dissociation of the weak C—N bond. The spin–orbit ratios of the NO fragment appear to be controlled by the topology, i.e. the details of the potential-energy surfaces involved. Intersystem crossing to the T₁(n,π*) state is found to affect the dynamics of all but the lowest S₁(n,π*) levels.

The C—N bond-dissociation energy of the title compound has been estimated as 14 300 ± 300 cm^–1(171 ± 3 kJ mol^–1) on the basis of fits of prior distributions to the observed rotational distributions of the NO photofragment.