Monday 01 October 2007
to 11:00 at
Åsa Larson (Theoretical chemistry, KTH)
Dissociative recombination (DR) is the process in which a molecular ion recombines with an electron, becomes neutral, and dissociates into two or more neutral fragments. Dissociative recombination of HCO+ is one of the key processes in the chemistry taking place in interstellar molecular clouds. We have recently undertaken a theoretical treatment of this reaction at low collision energies.
During the last decades there has been a debate on the mechanism which controls the DR of HCO+. We have found that there is no electronic state with a potential that crosses the ionic ground state potential close to its minimum, a usual requirement for the Direct Mechanism of DR. The absence of any curve-crossings is confirmed both by structure calculations, using the Multi Reference Configuration Interaction method, as well as electron scattering calculations, using the Complex Kohn variational method. The DR of HCO+ at low collision energies is believed to go through high lying neutral HCO Rydberg states, a process often referred to as the Indirect Mechanism. In order to describe this reaction, we find that it is important to include the Renner-Teller effect which will induce a vibronic coupling between the electronic and vibrational bending motions of the molecule. This type of Renner-Teller coupling has never been included in studies of dissociative recombination before.