Dissociative recombination of H 3 + : progress in theory

Abstract
Dissociative recombination is the main destruction process for ground–state H3+ in diffuse interstellar medium. Experiments agree on relatively large cross–sections for this reaction. Time–dependent two–dimensional calculations confirm the experimental results at high energy as well as the observed predissociation rates of H3 Rydberg states, due to non–adiabatic interactions. However, the value for low–energy crosssection, deduced from the predissociation rates by an extrapolation procedure, is about four orders of magnitude lower than the measured one. A calculation based on multichannel quantum defect theory suggests that an indirect non–adiabatic process may prevail in this case. The cross–section increases by orders of magnitude compared with the extrapolated value when indirect couplings via apparently ineffective channels are properly considered. We discuss how this channel–mixing mechanism can be effective in the case of H3+, and show encouraging results stressing the role of Rydberg series or ‘closed channels’. We also discuss possible three–dimensional effects that could enhance the process at low energy.

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