A study of the dynamics of UV laser photolysis of NOCl and NOBr

The photodissociation of NOCl and NOBr using lasers operating at 193 (ArF), 249 (KrF), 308 (XeCl), and 337 nm(N₂) has been studied under collisionless conditions by measuring the infrared fluorescence of the NO product. Little difference between the results for NOBr and NOCl was observed and all results indicate a linear dependence of photodissociation yield on laser power. The extent of NO vibrational excitation observed was quite large in photodissociation utilizing the ArF and KrF laser lines, with states up to v ≥ 16 observed with ArF and up to v ≥ 14 with KrF. The XeCl and N ₂ lines produced much less NO excitation, up to v ≥ 5. Statistical, half-collision, and Franck-Condon models of the photodissociation dynamics were studied, with best agreement with experiment for dissociation at 193 and 249 nm being obtained using a Franck-Condon model. An excited potential function for NOCl in which the NO properties were taken to be close to that of NO(⁴Π) was found to predict the shape of the dissociated NO vibrational distribution accurately at both 193 and 249 nm. Photolysis at 308 and 337 nm could also be explained by a Franck-Condon model using the NO(A ²Π) state to model the NOCl excited state.