FORMALDAZINE PHOTODISSOCIATION AND THE PAIR FORMATION OF H2CN RADICALS

The dissociation of formaldazine, H2CN-NCH2, following excitation at 193 nm has been studied by molecular beam photofragment translational spectroscopy. The only primary process, H2CN-NCH2 --> 2H2CN, takes place within a rotational period (almost-equal-to 10(-12) s) of the parent molecule and leads to the formation of H2CN radical pairs. The low translational energy release of merely 22% of the available energy indicates predissociation and furthermore implies that most of the nascent radicals possess enough internal energy to overcome the barrier E* of the reaction H2CN --> H + HCN. Based on the translational energy distribution P(E(T),H2CN) and the threshold energy E* = 30 kcal/mol, it is estimated that for 66% of the H2CN radical pairs both members decay and for 33% one partner is stable while the other one decays. Hence, after absorption of a photon approximately 80% of the H2CN radicals undergo a secondary dissociation step to HCN and H atoms.