NONADIABATIC COLLISIONS OF PROTON WITH CO AND O2 MOLECULES : A QUANTUM MECHANICAL STUDY

Abstract

Nonadiabatic phenomena are ubiquitous in nature. The dynamics of proton-molecule collisions often evolve on highly coupled electronic potential energy surfaces leading to inelastic and charge transfer processes. In this thesis, we have investigated the quantum dynamics of energy transfer processes involving the inelastic vibrational excitations and the vibrational charge transfer collisions in the H+ + CO and the H+ + O2 systems on our newly obtained quasi-diabatic ab initio potential energy surfaces for collision energies 0-30 eV and compared the collision attributes with the earlier theoretical results as well as the available stateto- state experimental data obtained from the molecular beam study and H+/H energy-loss spectra. We have described the computational details of the ab initio potential energy surfaces at the configuration interaction level of accuracy employing the correlation consistent polarized valence triple zeta basis sets. We report the details of time-independent quantum dynamics calculations for the inelastic vibrational excitations and vibrational charge transfer processes under the framwork of vibrational close-coupling rotational infinite order sudden approximation. To the best of our knowledge the present ab initio global adiabatic and quasi-diabatic potential energy surfaces for the ground and the first excited electronic states for the H+ + CO system are being presented perhaps for the first time in the literature. The present theoretical results are found to be in good agreement with those of experiments for the inelastic vibrational excitations and they are in overall qualitative agreement for charge transfer channel in the experimental trend. It is suggested that quantitative agreement between theory and experiment can be achieved by modelling the dynamics as a three- and four-state process. For the H+ + O2 system. quantum dynamics with the two-state (the ground and the first excited electronic states) coupling yields results in general agreement with the experiments. Significant improvement is achieved when the dynamics is carried out with four-state (the ground and the lowest three excited electronic states) coupling. However, some quantitative agreement between theory and experiment is still lacking, which can be settled through an elaborate and more refined (over a fine mesh of molecular orientation) computations within the VCC-RIOSA framework. A summary of the present study is given at the end with the concluding remarks and the future direction of research followed by bibliography.