Investigating CO dissociation by means of coarse grained ab-initio rate constants

This paper discusses the application of a Coarse-Grain Quasi-Classical Trajectory method (CG-QCT) to the study of the thermal and chemical non-equilibrium processes of the CO(¹ Σ⁺) + O(³ P) system. The reduced order models that have been developed in the past years rely on the solution of bins moment equation in which the rate constants of the bins are obtained by averaging the state-specific rates contained in the groups. However, the CO ro-vibrational energy is quantized in more than 13500 energy levels and the computational effort required for computing such rates is extremely high. The methodology discussed in this work, then, allows the calculation of the bin rates without the need of computing the state-specific quantities. By applying the reduction technique to the QCT calculations, indeed, the initial conditions of the trajectories can be obtained through a stratified sampling, for which the energy levels groups represent the strata. Results have shown excellent agreement between the overall thermal dissociation rates obtained averaging over the bins and the thermal dissociation rates computed by Schwenke et al. by averaging over a Boltzmann distribution on the ro-vibrational levels. Moreover, the bins rates so computed have then been used for solving a 60 Bins Master Equation by means of a Coarse Grained Model (CGM) for CO(¹ Σ⁺) + O(³ P) system in heat-baths at different constant translational temperatures; the accurate representation of the relaxation dynamics, proper of the CGM method, allowed to highlight the contributions of the different processes involved and the presence of Quasi-Steady-States.