Rates for the Electron Impact Dissociation of Molecular Hydrogen

Abstract

At astrophysically relevant temperatures (below 15,000 K), electron impact dissociation of H2 occurs through the excitation of the dissociative b Σ state. We have calculated and parameterized the rates of dissociation as a function of electron temperature for the v=0-4 H2 vibrational states. The assumption that the v=0 rate approximates to the rate at local thermal equilibrium (LTE) is found to be seriously flawed. Instead, the rates are found to depend so critically on the initial vibrational level that dissociation from very high-lying vibrational levels must be included in calculations of the rate at LTE even at low temperature. An extrapolation procedure is used to approximate the rates for all of the higher vibrational levels (v=5-14), which are then used to calculate the LTE rate. The LTE rate is found to be around 2 orders of magnitude greater than the v=0 rate.