Time-Resolved InfraredAbsorption Studies of the Solvent-Dependent Photochemistry of ClNO.

The photochemistry of nitrosyl chloride (ClNO) dissolvedin cyclohexane is investigated using ultrafast time-resolved infrared(TRIR) spectroscopy. Following 266 nm photolysis, the photochemistryis measured by following changes in optical density at frequenciesspanning the NO stretch fundamental transition. A photoinduceddepletion in optical density is observed consistent with the depletionof ground-state ClNO. The depletion in optical density remains constantout to ∼50 ps demonstrating that ClNO photodissociation isnot followed by recombination of the Cl and NO photofragments. Inaddition, no evidence for the formation of the ClON photoisomer isobserved. These results stand in contrast to previous studies in acetonitrilewhere ClNO photolysis is followed by geminate recombination of Cland NO, and by the production of ClON. These differences in ClNO photochemistryare proposed to arise from the population of different excited-statescaused by solvent dependence of the ground-state potential energysurface minimum along the Cl–N stretch coordinate. Solvent-dependentvibrational relaxation and differences in strength of the solventcage are also proposed to contribute to the solvent-dependent photochemistry.Finally, these results are placed in the context of recent modelsof ClNO photochemistry and role of this compound in tropospheric ozoneproduction. [ABSTRACT FROM AUTHOR]