Ultraviolet photodissociation dynamics of carbon suboxide

The vibrational and rotational excitation of CO produced in the UV laser photodissociation of carbon suboxide, C3O2, has been investigated. The internal energy of CO was detected under collision-free conditions by means of a pulsed vacuum UV laser probe, employing a two-laser time-resolved approach. The C3O2 was photodissociated at 266, 248, and 193 nm. The CO photoproduct was found to be vibrationally and rotationally excited as compared with a room temperature thermal equilibrium CO distribution. The average rotational energy and vibrational energy of the CO were determined to be 1.9 ± 0.2 kcal mol−1 and 0.6 ± 0.2 kcal mol−1 respectively at 266 nm, 2.6 ± 0.1 kcal mol−1 and 2.0 ± 0.5 kcal mol−1 at 248 nm, and 2.8 ± 0.2 kcal mol−1 and 1.4 ± 0.6 kcal mol−1 at 193 nm. Statistical calculation assuming C3O2 → CO + C2O predicted substantially greater internal excitation in CO than was obtained experimentally. The CO internal energy increased with excitation wavelength; it could be crudely described by an impulsive model. The carbon atoms produced by the 193 nm photolysis of C3O2 were also probed by vacuum UV laser-induced fluorescence. Only ground state C(3PJ) was detected. The branching ratio between carbon atom and C2O radical formation following 193 nm excitation of C3O2 was found to be 6% ± 3%.