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 (v₃) 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.