Radiative association of He : the role of quartet states

Rate coefficients for spontaneous and stimulated radiative association of the He molecular ion on the spin-quartet manifold are presented as functions of temperature considering the association with rotational-vibrational states of the lowest quartet electronic states and from the continuum states of the low-lying excited quartet states. The rate coefficients are obtained from the cross sections for radiative association, which are calculated by solving the Schrödinger equations for bound and continuum states supported by the corresponding Born-Oppenheimer potential energy curves. The rate coefficients for radiative association to the b state are several orders of magnitude larger than for radiative association to the c state. For all considered temperatures the spontaneous process is dominant. Stimulation of the radiative association by blackbody radiation has a significant influence only on the process at temperatures below 1000 K.