Executive Summary : | Investigation of complex nonadiabatic effects has become increasingly important in contemporary research in chemical dynamics. The present proposal aims a thorough theoretical study on these effects in the processes ranging from molecular spectroscopy to reactive chemical dynamics. As is well known the Born-Oppenheimer approximation completely breaks down in this situation and nuclei moves concurrently on more than one energetically accessible electronic potential energy surfaces. The singularity of the adiabatic electronic basis ceases to work and one requires to develop complementary quasi-diabatic electronic basis. The required electronic structure calculations will be carried out to develop potential energy surfaces to carry out nuclear dynamics study from first principles. Methods and algorithms will be developed in time-independent, time-dependent quantum mechanical and also classical framework. The developed methods will be applied to study Jahn-Teller and Renner-Teller effects in nonlinear and linear symmetric molecular systems, respectively. Electronic spectroscopy of polycyclic aromatic hydrocarbons and carbon chains will be studied in an attempt to search for the molecular carriers of diffuse interstellar bands and to aid in their assignments. Photodetachment spectroscopy of anionic boron clusters will be studied to elucidate their novel structure and bonding properties. Effect of fluorine atom substitution on the electronic excited state dynamics of organic hydrocarbons will be studied. Reactive dynamics of bi-molecular chemical systems will be studied on coupled multi-sheeted potential energy surfaces to elucidate their reaction and energy disposal mechanism. Photo-dissociation dynamics of bio-active organic molecules will be studied on coupled potential energy surfaces. The results of these studies will be compared with the observations in the modern experiments to provide fundamental understanding of the subjects as well as to guide new future experiments. The signatures of various effects imprinted in the recorded experimental spectrum will be unraveled. |