PHOTODISSOCIATION OF ALKYL NITRITES IN A MOLECULAR-BEAM - PRIMARY AND SECONDARY REACTIONS

The translational energy distributions P(ET) for the 248-nm photodissociation products (NO + RO) of isopropyl nitrite and tert-butyl nitrite have been measured with a molecular beam time-of-flight (TOF) apparatus. Previous experiments with methyl nitrite and ethyl nitrite have been repeated with higher resolution. The average photofragment translational energies of these four alkyl nitrites are in good agreement with those predicted by an impulsive model that treats the NO as a rigid fragment and the alkoxy radical as a soft fragment. Hence, and in contrast to the vibrational predissociation on the S1 potential energy surface, S2 dissociation is direct and involves no significant "vibrational-translational" coupling between the reaction coordinate rO-N and the rN=O coordinate. The width of the experimental P(ET) distributions decreases with increasing size of the alkoxy substituent. This result is discussed in terms of an anticorrelation between the internal energies of a fragment pair. Furthermore, the spontaneous secondary dissociation of isopropoxy and tert-butoxy photofragments was observed which yields CH3 radicals and acetaldehyde or acetone, respectively. The unimolecular decay of these alkoxy radicals confirms their relatively high internal energy as deduced from the primary P(ET) and it is shown that this decay occurs on a submicrosecond time scale. © 1990 American Chemical Society.