Photodissociation and radiative association of HeH+ in the metastable
  triplet state
  We investigate the photodissociation of the metastable triplet state of HeH+
as well as its formation through the inverse process, radiative association. In
models of astrophysical plasmas, HeH+ is assumed to be present only in the
ground state, and the influence of the triplet state has not been explored. It
may be formed by radiative association during collisions between a proton and
metastable helium, which are present in significant concentrations in nebulae.
The triplet state can also be formed by association of He+ and H, although this
process is less likely to occur. We compute the cross sections and rate
coefficients corresponding to the photodissociation of the triplet state by UV
photons from a central star using a wave packet method. We show that the
photodissociation cross sections depend strongly on the initial vibrational
state and that the effects of excited electronic states and non-adiabatic
couplings cannot be neglected. We then calculate the cross section and rate
coefficient for the radiative association of HeH+ in the metastable triplet
state.
