The collision-free photochemistry of methyl azide at 157 nm: Mechanism and energy release

Synchrotron radiation VUV-photoionization based photofragment translational spectroscopy was used to identify the primary and secondary photodissociation reactions of methyl azide (CH3N3) at 157 nm under collision-free conditions. Two primary dissociation channels are identified, leading to CH3 + N3 (the radical channel) and CH3N + N2 (the molecular elimination channel). The last channel is the major dissociation pathway, but unlike work at longer photolysis wavelengths, here, the radical channel exclusively produces the higher energy isomer cyclic-N3. Product time-of-flight data for both channels were obtained and compared with earlier work on methyl azide photochemistry at 193 nm based on electron impact ionization, allowing us to estimate a product branching ratio Φ C H 3 − N 3 Φ C H 3 N − N 2 = 2.3 % ± 0.6 % 97.7 % ± 0.6 % .