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Indirect Dissociative Recombination of LiH Molecules Fueled by Complex Resonance Manifolds
The LiH molecule is prototypical of the indirect dissociative
recombination (DR) process, in which a colliding electron destroys the molecule
through Rydberg capture pathways. This Letter develops the first quantitative
test of the Siegert state multichannel quantum defect theory description of
indirect DR for a diatomic molecular ion. The R-matrix approach is adopted to
calculate ab-initio quantum defects, functions of the internuclear distance
that characterize both Rydberg states and the zero-energy collisions of
electrons with LiH ions. The calculated DR rate coefficient agrees
accurately with recent experimental data (S. Krohn et al, Phys. Rev. Lett. 86,
4005). We identify the doorways to fast indirect DR as complex resonance
manifolds, which couple closed channels having both high and low principal
quantum numbers. This sheds new light on the competition between direct and
indirect DR pathways, and suggests the reason why previous theory
underestimated the DR rate by an order of magnitude.Comment: Submitted to PR
Photofragmentation of the H_3 molecule, including Jahn-Teller coupling effects
We have developed a theoretical method for interpretation of photoionization
experiments with the H_3 molecule. In the present study we give a detailed
description of the method, which combines multichannel quantum defect theory,
the adiabatic hyperspherical approach, and the techniques of outgoing Siegert
pseudostates. The present method accounts for vibrational and rotation
excitations of the molecule, deals with all symmetry restrictions imposed by
the geometry of the molecule, including vibrational, rotational, electronic and
nuclear spin symmetries. The method was recently applied to treat dissociative
recombination of the H_3^+ ion. Since H_3^+ dissociative recombination has been
a controversial problem, the present study also allows us to test the method on
the process of photoionization, which is understood better than dissociative
recombination. Good agreement with two photoionization experiments is obtained.Comment: 10 figure
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