Pyrazine: Supercollisions or simple reactions?

Photodissociation of 1,4 diazine (pyrazine) following 248 nm (S2←S0) and 308 nm (S1←S0) excitation has been studied by photofragment translational spectroscopy. While the latter wavelength was inefficient at generating reactive products, the former wavelength afforded a rich variety of fragments, the most translationally energetic being HCN carrying up to 36 kcal/mol. The implications of this reactive mechanism toward interpretation of vibrational energy transfer experiments from hot ground state pyrazine are considered. The absolute quantum yields φ(248 nm, 27-A)=0.40±0.10, φ(248 nm, 27-B)=0.08±.02, φ(308 nm, 27-B′)=0.003±.001 and the two corresponding translational energy distributions are presented.