Nonstatistical CO product distributions from the hot H-atom reaction, H+CO2→OH+CO

Abstract

The hot H-atom reaction, H+CO2→OH+CO is investigated under several initial conditions designed to vary the angular momentum of the CO2 reactant. The translationally hot H atoms are produced by photodissociating H2S at 193 nm, resulting in a reaction exoergicity of ∼120 kJ mol−1. The internal energy in the CO product is monitored by laser-induced fluorescence in the VUV spectral range. Under near-nascent conditions we report the rotational distributions of CO in v″=0 under CO2 reactant ‘‘temperatures’’ of 300, 70 and 40 K. Also reported are the rotational distributions of CO in v″=1 at 300 K and 70 K and the population ratios of [v″=1]/[v″=0] at both initial CO2 temperatures. Three distinctively ‘‘dynamical’’ aspects of the potential energy (PE) surface are exhibited in this set of experiments: (i) As the CO2 reactant is cooled, a cooling of the CO distribution is seen which suggests the reaction intermediate does not live long enough to randomize its internal energy. (ii) We report a coupling of vibrational and rotational excitation in the CO product indicated by a ‘‘hotter’’ rotational energy in v″=1 than v″=0 at 300 K. (iii) In addition, we report different [v″=1]/[v″=0] ratios at the two CO2 initial temperatures. Contrary to nearly all indications from measurements on the OH product, the CO product is rich in ‘‘nonstatistical’’ behavior.