The radiative association of He+ and He and H(+) and H

Abstract

The rate coefficient for the radiative association of He+ and He to form He(2+) is determined for temperatures T between 20 K and 500,000 K. It can be represented by a given relation to within 25 percent applicable up to 50,000 K. It is about an order of magnitude less than the rate coefficient for the radiative association of H(+) and H to form H(2+). Cross sections for the He(2+) and H(2+) reactions calculated using a fully quantum-mechanical method reveal weak resonance features at low energies. Implications of the He(+) + He radiative association process are discussed briefly in connection with the chemistry of supernova ejecta, planetary