Calcium-hydrogen interactions for collisional excitation and charge transfer
Résumé
The accurate highly correlated ab initio calculations for ten low lying covalent 2+ states of CaH
molecule, and one ionic Ca+H state, are performed using large active space and extended basis set,
with special attention to the long-range (6-20 Å) region where a number of avoided crossings between
ionic and covalent states occur. These states are further transformed to a diabatic representation using
a numerical diabatization scheme based on the minimization of derivative coupling. This results in a
smooth diabatic Hamiltonian which can be easily fit to an analytic form. The diagonal elements of the
diabatic potentials were then empirically corrected to reproduce experimental dissociation energies.
Though the emphasis is on the asymptotic region, the obtained spectroscopic constants are in good
agreement with available experimental and theoretical data. The resulting analytical Hamiltonian,
after back transformation to adiabatic representation, is used to obtain cross sections for different
inelastic processes using both the multichannel and the branching probability current approaches.
It is shown that while for most intense transitions both approaches provide very close results, the
multichannel approach underestimates the cross sections of weak transitions, as a consequence of
the short-range avoided crossings that are accounted for only in the branching probability current
method.