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(³P_J) was detected. The branching ratio between carbon atom and C₂O radical formation following 193 nm excitation of C₃O₂ was found to be 6% ± 3%.