Electronic structure and dynamics of O(3P)+CO(1Σ+) collisions

Abstract

The potential energy surfaces of the three lowest electronic triplet states of CO2 which lead to O(3P)+CO(1Σ+), 3A′, 1 3A″, and 2 3A″, have been computed at the completeactive-space-self-consistent-field plus second-order perturbation theory (CASSCF-MP2) level with a modest 631+G(d) basis. Potential energy surfaces are fit with a global functional form. The 3A′ state has a well 0.9 eV deep and the 1 3A″ state has a 0.2 eV well with respect to the O(3P)+CO(1Σ+) dissociation threshold. The 3A′ and 1 3A″ states are both bent at their minima and have a barrier at 0.2 eV and 0.3 eV above threshold, respectively. The 2 3A″ state is mostly repulsive, and has a saddle at C2v geometries. We have run classical trajectory calculations for O(3P)+CO(1Σ+) collisions using these surfaces. Results agree well with available vibrational relaxation and oxygen atom exchange measurements except at low temperature. Comparisons are also made with measured vibrational excitation cross sections and infrared emission spectra of the nascent CO products at 3.4 eV collision energy. These results show a high degree of vibrational and rotational excitation with a nearly statistical population which is evident in a distinct spectral “bandhead” signature. Analysis of the trajectories show that almost all collisions which lead to oxygen atom exchange and/or vibrational energy transfer occur when the O(3P) approaches the CO at OCO angles between 80° and 140°, passes over the barrier and through the wells of the 3A′ and 1 3A″ states, and interacts with the repulsive wall of the carbon end of the CO nearly perpendicular to the CO bond.