Dissociative recombination of H3+:: progress in theory

Dissociative recombination is the main destruction process for ground-state H(3)(+) 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 Hg Rydberg states, due to non-adiabatic interactions. However, the value for low-energy cross-section, 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 ho iv this channel-mixing mechanism can be effective in the case of H(3)(+), 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.