Dissociative recombination of H+2, HD+, and D+2 by collisions with slow electrons

Abstract

Using the multichannel quantum defect theory (MQDT), dissociative recombination of H+2, HD+, and D+2 via the two-electron excited superexcited state 1Σg(2pσu)2 is studied for each specified initial vibrational state vi (≲4) of molecular ions at low electron energies 0.02≲E≲1.0 eV. The necessary basic physical quantities, electronic coupling V(R) and quantum defect as a function of internuclear distance R, are obtained from our previous scattering calculations. As a by-product we have also obtained the singlet scattering d-wave partial cross sections for the various vibrational transitions of molecular ions by electron impact. It is found that the Franck–Condon like factor between vibrational state and dissociative continuum is most decisive in characterizing the overall magnitude and energy dependence of the cross sections. Even the vibrational transitions occur predominantly via the dissociative superexcited state. This suggests that the preionization mechanism of the states of the 1Σg symmetry is very different from that of 1Σu and 1Πu in the vicinity of ionization threshold.