AB initio potential energy surfaces and and quantum dynamics of CS and CO collosions in cold and ultracold regions

Abstract

In this thesis, we have investigated the quantum dynamics of interstellar molecules, CS and CO for collision energies in cold, of astrophysical interest to ultracold regimes, less than 1 mK. We have reviewed the theoretical studies on colliding systems of interest. We have obtained new potential energy surfaces computed using ab initio multiref erence configuration interaction method and augmented correlation consistent polarized valence quadruple zeta basis set for HCS+ and HCS species. The analytic fits for the ground state surface has been elucidated with the stability of the species with their isomers is discussed. Quantum dynamics of nonadiabatic collisions between H − CS+ system has been studied for collision energies in the range of 2 − 8 eV that results in inelastic and charge transfer using the ground and the low-lying excited electronic one-dimensional potential energy surfaces for collinear and perpendicular approaches of H towards CS+. The study has been performed using time-dependent wave packet dynamics involving two and three electronic states. Probabilities for the inelastic and charge transfer is computed and found to be maximum when colliding in collinear configuration of HCS+. Time-independent quantum dynamics has been modeled on the ground state rigid rotor surfaces of systems, H collisions with CS+ and CS. Rotational excitations are studied using close-coupling method and dynamical attributes such as integral cross sections and corresponding rate coefficients for each excitation has been computed. We have investigated rotational quenching study for H+ − CO, H − CS+ and He − CS systems in the cold and ultracold regimes. The range of rotational deexcitations has been extended down to temperatures of 10−5 K to understand the behaviour of molecules with dynamics at the lowest of temperatures. The propensity for rotational transitions for all the systems has been discussed in detail. A summary of the present work is given at the end of the thesis along with the conclusions and the future direction of research followed by bibliography.