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_CH Φ_CH =2.3%±0.6%97.7%±0.6%.