Photolysis of oxalyl chloride (ClCO)2 at 193 nm: emission of CO(v<or=6, J<or=60) detected with time-resolved Fourier-transform spectroscopy.

Upon photolysis of oxalyl chloride at 193 nm, time-resolved and rotationally resolved emission of CO(v<or=6, J<or=60) in the spectral region 1850-2350 cm(-1) was detected with a step-scan Fourier-transform spectrometer under nearly collisionless conditions. Boltzmann-type rotational distributions of CO correspond to temperatures 3520+/-110 (v=1) to 2300+/-610 K (v=6), with an average rotational energy of 23+/-2 kJ mol(-1). The average vibrational energy of CO is estimated to be 26+/-4 kJ mol(-1) according to observed vibrational populations of v=1-6 and that of v=0 predicted with a surprisal analysis. Combining the average internal energy of CO determined in this work and average translational energies of photofragments Cl and CO determined previously by Hemmi and Suits, we propose a four-body dissociation mechanism producing one pair of translationally rapid and internally excited CO and one pair of translationally rapid Cl, each with similar energies, to account for the energy balance. Formation of translationally slow ClCO, Cl, and CO reported previously by Hemmi and Suits might be rationalized with a second channel involving emission of electronically excited intermediates. We observed no emission of ClCO near 1880 cm(-1), indicating that surviving ClCO has little vibrational excitation in the C-O stretching mode. (c) 2004 American Institute of Physics.