  We use quantum and classical adiabatic capture theories to study the chemical
reaction Li + CaH -> LiH + Ca. Using a recently developed ab initio potential
energy surface, which provides an accurate representation of long-range
interactions in the entrance reaction channel, we calculate the adiabatic
channel potentials by diagonalizing the atom-molecule Hamiltonian as a function
of the atom-molecule separation. The resulting adiabatic channel potentials are
used to calculate both the classical and quantum capture probabilities as a
function of collision energy, as well as the temperature dependencies of the
partial and total reaction rates. The calculated reaction rate agrees well with
the measured value at 1 K [V. Singh et al., Phys. Rev. Lett. 108, 203201
(2012)], suggesting that the title reaction proceeds without an activation
barrier. The calculated classical adiabatic capture rate agrees well with the
quantum result in the multiple partial wave regime of relevance to the
experiment. Significant differences are found only in the ultracold limit (T <
1 mK), demonstrating that adiabatic capture theories can predict the reaction
rates with nearly quantitative accuracy in the multiple partial wave regime.
