Theoretical investigation of H atom tunneling in Catecholate Monoanion: A combined time-independent and time-dependent quantum mechanical study

Abstract

This thesis presents a combined time-independent and time-dependent quantum mechanical study of a system, Catecholate Monoanion (CM) for the study of H atom tunneling. It has an intramolecular H bond leading to a symmetric double well potential. Tunneling in a symmetric double well potential leads to lifting of degeneracy and splitting of energy levels. This has been an attraction for physicists and chemists for over 80 years. As the molecular process involves many degrees of freedom, the tunneling problem is multidimensional. Experimental works have indicated mode-specific tunneling effects, i.e. with selective excitation of a mode, tunneling splitting may enhance, decrease or have no effect [1–3]. These seemingly counterintuitive results have led to theoretical studies to understand the mechanism of the tunneling process. Several works with approximate approaches and exact variational treatments have indicated that incorporating multiple degrees of freedom is necessary for a correct description of these problems. Three systems, namely malonaldehyde, formic acid dimer and tropolone are very well-explored for mode-specific tunneling splittings, which includes recent theoretical studies [4–6]. These calculations indicate that the role of frequency, coupling strength and symmetry of different modes is important for these systems and results can be non-trivial. CM is a system bigger than the most extensively studied malonaldehyde, with the possibility of serving as a prototypical system where exact treatment of various vibrations may be carried out without approximation. In this thesis, we have studied CM from both eigenstate calculation and dynamics perspectives. The former allows an understanding of the trends of mode-specific tunneling splittings in CM, while the dynamical studies help unravel the coupling mechanism that leads to enhancement or suppression of tunneling in this system.