Electronically excited nitric oxide by vacuum ultraviolet photodissociation of nitroso-compounds and nitrites

The gas-phase photolysis of CF₃NO and EtONO at 123 and 147 nm and of Bu^tNO at 147 nm gives rise to electronically excited nitric oxide which fluoresces. The strongest emission is that of the A ²S⁺-X²II transition (?-bands), although other transitions are also observed. The vibrational level populations in the NO(A²S⁺) state show some correlation with the energy of the incident radiation and the strength of the R-NO bond. Addition of helium to the CF₃NO or EtONO produces an enhancement of emission from the v' = 2 and 3 levels of the A²S⁺ state, while emission from v' = 0 and 1 is almost unchanged. Addition of low pressures of N₂ and H₂ also gives some enhancement of v' = 2 and 3. These observations are discussed in terms of the possible excited states of NO produced during the photolysis, and the deactivating effects of the added gas. Photolysis of ONCN at 147 nm yields electronically excited cyanide radicals and the (B²S-X₂S) violet bands are observed. There is evidence for considerable rotational excitation of the CN radical, an effect well known in the vacuum u.v. photolysis of other cyanides, e.g. ICN.