The concerted photodissociation of azomethane at 193 nm Original Research Article

The 193 nm photodissociation of azomethane CH3N2CH3→CH3+N2+NH3 has been investigated by photofragment translational spectroscopy. The time-of-flight (TOF) distribution of the CH3 photogragments consists of a single and relatively narrow peak which indicates that the two methyl radicals are formed with equal or very similar velocity distributions. Based on this result and on the observed TOF distribution of the N2 fragment, the rupture of the two CN bonds is shown to be consistent with a concerted mechanism with the possibility of a symmetric three-body decay. Furthermore, the concerted mechanism implies that dissociation is preceded by rapid isomerisation from the initial trans form to a gauche or cis type structure. The isotropic (β≈0) angular distributions of CH3 and N2 are consistent with an electronic transition moment being oriented parallel to the NN bond.