PHOTODETACHMENT OF LINEAR SYSTEMS

Abstract

This dissertation is focused on the photodetachment of linear homo- nuclear negative molecular ions in and in the absence of external field. A new approach of N-center model (NCM) and theoretical imaging method are employed to study these systems. The detached-electron wave function from a linear tetra-atomic negative ion is first formulated as a superposition of the electron waves originating from the four cores of the ion. The ion behaves as a coherent source of the detached electron waves shined with polarized laser light. The detached electron flux is then evaluated on an observation plane placed at a very large distance from the system. The strong oscillations in the detached-electron flux reveals quantum interference effects. The total photodetachment cross section is evaluated by integrating this electron flux for all angles. It is observed that the amplitude of oscillations varies as we change the laser orientation with molecular axis. It is maximum when polarized laser light is parallel to the molecular axis and then it gradually decreases with the increase in the angle. Eventually it becomes zero as the polarization of the laser light is perpendicular to the molecular axis. The cross section is also found to be dependent on the interatomic distance. If the interatomic distance is very large then the amplitude of oscillations is negligibly small. This is due to the fact that at very large interatomic distance, the linear tetra-atomic molecule is broken into three neutral atoms and an atomic negative ion and under this condition the total cross section shows smooth behavior. Theoretical imaging method is used to investigate the surface induced effects in the photodetachment cross section of H 2 − . The photodetachment of H 2 − in the vicinity of a soft reflecting wall is investigated and analytical expressions for the differential and total cross sections are derived. It has been iiobserved that the wall induces oscillatory structure in the photodetachment cross section of H 2 − and the total cross section is similar to the cross section of a tetra-atomic negative ion. The asymptotic cross section of our result is identical to the already published results of the closed orbit theory. We hope that our theoretical studies may be helpful to understand the structure and dynamics of linear tetra-atomic systems like C 2 H 2 − , Ar 2 HF − , GeC 2 N − , C 2 HS − as well as H 2 − near an interface in the photodetachment microscopy experiments.