Direct formation of CH2 (b̃ 1B1) in the near-UV photodissociation of diazirine

A prompt, long-lived, and red fluorescence has been observed in the photodissociation of the jet-cooled diazirine (H2CN2) excited at the origin (322.96 nm) of the S1←S0 transition. The fluorescence decays (∼16 μs) and range (>575 nm) indicate that the emitting species is the electronically excited singlet methylene, CH2 (b̃ 1B1). The linear dependence of the fluorescence intensity on the photolysis laser power strongly supports that the fluorescing CH2 (b̃ 1B1) is produced directly from the first excited singlet state of diazirine. The observation that the fluorescence appears in the visible wavelength region indicates that the CH2 (b̃ 1B1) fragments are highly vibrationally excited.