Abstract

The first principle based Beyond Born-Oppenheimer (BBO) theory [1-3] is presented for the construction of highly accurate potentially coupled surfaces to explore photoelectron (PE) spectra of NO3- and 1,3,5-C6H6F3 [4-5], reactive scattering processes of H3 + and HeH2+ [6-9], and phase transition phenomena of perovskites [10,11]. Jahn-Teller (JT) and Renner-Teller (RT) types of conical intersections (CIs) along with Pseudo Jahn-Teller (PJT) interactions and semi-circular CI seams are

investigated. [4-6,8,10,11] Theoretically calculated spectra show peak by peak correspondence with the experimental and other theoretical findings. [4-5, 10] Reaction attributes (reaction probabilities, cross-sections and/or rate constants) of D++H2 and He+H2+ processes obtained from scattering dynamics over global diabatic surfaces of H3+ [7] and HeH2+ [9] systems, respectively, exhibit accord

with the experimentally measured ones for non-zero total angular momentum situations. Optical spectra of LaMnO3 shows anomalous temperature dependence around the Neel temperature. This behaviour could be due to JT effect both in ground and excited states. Such observations have been investigated theoretically using model [12] as well as ab initio [10] potential energy surfaces (PESs)

of MnO69- to interpret the experimental spectra due to the excitations of the quantum rotors. On the other hand, we are on the process of constructing the BBO based diabatic Hamiltonian of TiO68- [11] to compute roto-vibrational vis-á-vis PE spectra.