The kinetic theory of H2 dissociation

Abstract

Collisional dissociation of interstellar molecular hydrogen may be suppressed at low densities by radiative stabilization of high vibrational level populations. The rate coefficient for H2 dissociation is computed with a master equation eigenvalue approach, including collisional excitation and dissociation from all 15 vibrational levels. The rates are sensitive to vibrational 'ladder climbing', multiquantum vibrational excitations, and collisional dissociation from low vibrational levels. Including these effects, it is found that the low-density dissociation rate at 4500 K is only suppressed by a factor of a thousand from the high-density limit. Analytic fits to the dissociation and radiative cooling rates are provided over a range of densities and temperatures.