ARTICLES Distribution of Vibrational States of CO2 in the Reaction O(1D) + CO2 from Time-Resolved Fourier Transform Infrared Emission Spectra

A mixture of O3 and CO2 was irradiated with light from a KrF laser at 248 nm; time-resolved infrared emission of CO2 in the region 2000-2400 cm-1 was observed with a Fourier transform spectrometer. This emission involves one quantum in the asymmetric stretching mode (ν3) of CO2 in highly vibrationally excited states. The band contour agrees satisfactorily with a band shape calculated based on a simplified polyad model of CO2 and a vibrational distribution estimated through a statistical partitioning of energy of ∼13 000 cm-1, ∼3100 cm-1 smaller than the available energy, into the vibrational modes of CO2. From this model, approximately 44 % and 5 % of the available energy of O(1D) + CO2 is converted into the vibrational and rotational energy of product CO2, respectively, consistent with previous reports of ∼50 % for the translational energy. An extent of rotational excitation of CO2 much smaller than that expected from statistical calculations indicates a mechanism that causes a small torque to be given to CO2 when an O atom leaves the complex CO3 on the triplet exit surface of potential energy, consistent with quantum-chemical calculations