Calculated rates for the electron impact dissociation of molecular hydrogen: mixed isotopomers and scaling laws

Following our calculations of electron impact dissociation rates of molecular H-2, D-2 and T-2 (Trevisan and Tennyson 2002 Plasma Phys. Control. Fusion 44 1263-76), calculations for the mixed isotopomers HD, HT and DT have been made. Total cross sections and energy differential cross sections at threshold energies as a function of vibrational states (nu) for HD: nu = 0-5, for HT: nu = 0-5 and for DT: nu = 0-7 are calculated for the electron impact dissociation through excitation to the b(3)Sigma(u)(+) excited electronic state, which is the dominant dissociation process at such energies. The rates of dissociation as a function of electron temperature for each state are parametrized. Coinciding with our previous results, near-threshold rates are shown to be so critically dependent on the vibrational level that dissociation from very high-lying vibrational levels must be included in calculations of the rate at local thermal equilibrium (LTE) even at low temperature. Rates for the higher vibrational levels are obtained by extrapolation following the procedure discussed in our previous publication, and are then used to calculate the LTE rate. The LTE rate is an order of magnitude greater than the nu = 0 rate. A scaling law for the electron impact dissociation cross sections of vibrationally excited H-2 and its isotopomers has been derived.