Quasi-classical trajectory study of the dynamics of the reaction O( 3P)+CS 2(X 1∑ +g)→CS(X 1∑ +)+SO(X 3∑ −) using two model potential energy surfaces

Abstract

The dynamics of the O( 3P)+CS 2(X 1∑ + g)→CS(X 1∑ ++SO(X 3∑ −) reaction at relative collision energies in the range 3.2–12.2 kcal/mol has been studied by means of the 3D quasi-classical trajectory method. Two empirical analytical models for the ground triplet surface, based on semiempirical, ab initio and spectroscopic data have been used. The first model surface fits a reaction energy profile that presents only the cis-OSCS ( 3A″) minimum found in two different quantum calculations. The second model surface exhibits a typical reaction energy profile with only an early low energy barrier located at a collinear saddle point. Comparison of different attributes with available experimental data indicates the first surface to be in general in much better agreement with experimental data than the second one. The reaction proceeds mainly through a complex mode, even though a predominant SO forward scattering in the c.m. system exists. The high fraction of available energy release as product translation (≈ 49%) for this surface is, however, even far from the experimental value (≈27%), indicating that additional modifications should be introduced in the surface to account for this value. The reaction cross section calculated at the lowest relative translational energy studied (1.52±0.27 Å 2) is quite close to the value estimated from crossed molecular beams experiments (1.1±0.4 Å 2). Reactivity increases with reactant translational and vibrational excitations and diminishes with rotational excitation. Excitation in the CS 2 symmetric stretch enhances reactivity more efficiently that in the asymmetric stretch as was previously found in a collinear trajectory study.