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