Quenching of Li low-n Rydberg atoms by ground-state He atoms: A low-energy molecular-state calculation

Total cross sections for quenching of low-n Rydberg states of Li (n<10, l=0) in collision with the ground state He have been calculated in the low-energy region (v<~0.1a.u.) by employing the molecular orbital approximation. Results for the total depopulation of the parent states, along with those for excitation and de-excitation mechanisms have been presented. Present cross sections exhibit the low-energy Stueckelberg oscillations. Using a model two-state calculation we present a detailed comparative study between the quantum-mechanical and semiclassical findings. Except at very low energies, the semiclassical cross sections agree nicely with their quantum counterparts. The reaction rates at thermal energies are also reported.