Structured absorption spectrum and vibrational state-selectivity in the photodissociation of methyl nitrite in the near-UV

The gas-phase electronic absorption spectrum of methyl nitrite (CH₃ONO) in the near-UV has been re-examined. Both temperature dependence and comparison of the vibrational structure with nitrous acid (HONO) and tertiary-butyl nitrite (t-BuONO) show that syn-anti isomerism leads to two shifted, overlapped band systems. The origin of the prominent S₁ N=O stretch progression of the syn-rotamer has been re-assigned to the medium strong feature at 364.3 nm. The vibrational energy disposal into NO is reported for photolysis of jet-cooled CH₃ONO at 387,380 and 355 nm. Photolysis at all three wavelengths favours vibrational disposal into NO (v?=0). All currently available experimental results indicate a preference for an adiabatic or direct mechanism as the predominant dissociation route. © 1992.