Photolysis of oxalyl chloride (ClCO)₂ at 248 nm: Emission of CO(ν′ ≤ 3, J′ ≤ 51) detected with time-resolved Fourier transform spectroscopy

Upon photolysis of oxalyl chloride at 248 nm, rotationally resolved emission of CO (ν ≤ 3) in the spectral region 1900-2300 cm^-1 was detected with a step-scan time-resolved Fourier transform spectrometer under nearly collisionless conditions. Boltzmann-like rotational distributions of CO (ν = 1 and 2) correspond to temperatures ∼2290 = 100 and 1910 ± 130 K, respectively, with average rotational energy of 16 ± 2 kJ mol^-1; several lines of CO (ν = 3) were also observed, but their weak intensity precludes quantitative analysis. The average vibrational energy of CO is estimated to be 10 ± 3 kJ mol^-1 according to observed vibrational populations of ν = 1 and 2 and that of ν = 0 and 3 predicted with surprisal analysis. Combining the average internal energy of CO determined in this work and average translational energies of photofragments Cl, CO, and ClCO determined previously by Suits and co-workers, we derived a revised energy balance. We observed no emission of ClCO near 1880 cm^-1, indicating that ClCO (ν = 1) decomposes rapidly and that surviving ClCO has little vibrational excitation in the CO stretching mode. Most CO produced from decomposition of ClCO is in its vibrational ground state with small rotational excitation, undetectable with our technique.