Collision-free photochemistry of methylazide: Observation of unimolecular decomposition of singlet methylnitrene.

Methylazide photolysis at 248 nm has been investigated by ionizing photofragments with synchrotron radiation in a photofragmentation translational spectroscopy study. CH₃N and N₂ were the only observed primary products. The translational energy release suggests a simple bond rupture mechanism forming singlet methylnitrene, ¹CH₃N, and N₂. Thus, these experiments reveal the unimolecular decomposition of this highly unstable species. We explain our observations through a mechanism which is initiated by the isomerization of ¹CH₃N to a highly internally excited methanimine H₂C==NH isomer, which decomposes by 1,1-H₂ elimination forming HNC+H₂ as well as sequential H-atom loss (N–H followed by C–H bond cleavage), to form HCN. No evidence for dynamics on the triplet manifold of surfaces is found. [ABSTRACT FROM AUTHOR]