Photofragmentation translational spectroscopy of methyl azide (CH3N3) photolysis at 193 nm: molecular and radical channel product branching ratio.

We describe molecular-beam photofragment translational spectroscopy (PTS) experiments using electron impact (EI) ionization product detection to investigate the 193 nm photodissociation of methyl azide (CH3N3) under collision-free conditions. These experiments are used to derive the branching ratio between channels 1 and 2 [(1) radical channel: CH3N3 + h nu (lambda = 193 nm) -> CH3 + N-3; (2) molecular channel: CH3N3 + h nu (lambda = 193 nm) -> CH3N + N-2], which have been reported in a previous VUV-photoionization based PTS study.(1) Using electron impact ionization cross sections and ion fragmentation ratios for the various detected products, we derive the branching ratio (XCH3-N3)/(XCH3N-N2) = (0.017 +/- 0.004)/(0.983 +/- 0.004). Based on analysis of the kinetic energy release in the radical channel, we find that the cyclic form of N-3 is the dominant product in the radical channel. Only a small fraction of the radical channel produces ground state linear N-3.