CO INTERNAL EXCITATION FROM THE REACTION - H+CO2-]CO+OH

Time-resolved infrared diode laser absorption spectroscopy has been used to probe CO internal excitation following 193 nm photolysis of 300 K H2S/CO2 samples. Vibrations and rotations are colder than statistical, i.e., E(int) (CO) is only approximately 1500 cm-1 even though approximately 10 000 cm-1 is available for product excitations, assuming modest collisional deactivation of the hot H atoms that undergo reaction. A [upsilon = 1]/[upsilon = 0] ratio of approximately 0.4 is obtained and there is essentially no population at upsilon greater-than-or-equal-to 2. Both the upsilon = 0 and 1 rotational distributions are cold, peaking at J(max) approximately 11 and 13, respectively. The vibrational distribution is nascent while the rotational distributions may be partially relaxed, but not enough to alter the main conclusions. Combined with earlier results for OH internal excitations and center-of-mass (CM) kinetic energies, we conclude that at high collision energies there is a propensity toward product CM kinetic energy. In this regime, the reaction cross section rises rapidly with energy and statistical unimolecular rate theory is not applicable, even with a HOCO dagger intermediate.