Dissociative recombination of H-3(+): progress in theory

Dissociative recombination is the main destruction process for ground-state H-3(+) in diffuse interstellar medium. Experiments agree on relatively lar ge cross-sections for this reaction. Time-dependent two-dimensional calcula tions confirm the experimental results at high energy as well as the observ ed predissociation rates of Hg Rydberg states, due to non-adiabatic interac tions. However, the value for low-energy cross-section, deduced from the pr edissociation 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 p revail in this case. The cross-section increases by orders of magnitude com pared with the extrapolated value when indirect couplings via apparently in effective channels are properly considered. We discuss ho iv this channel-m ixing mechanism can be effective in the case of H-3(+), and show encouragin g results stressing the role of Rydberg series or 'closed channels'. We als o discuss possible three-dimensional effects that could enhance the process at low energy.