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.