The validity of the local approximation in Penning ionization as studied by model calculations

Abstract

In the theoretical treatment of Penning ionization A* + B→A+ B+ + e− it is standard to describe the nuclear motion in the entrance channel A* + B by a local complex potential. The motivation stems from the conceptual simplicity of the local potential operator compared to the nonlocal formulation and from the necessity to economize in computer time. In all practical calculations the local ansatz has worked well so far. Observed discrepancies between calculated and experimental data have never unambiguously been assigned to a failure of the local approximation. However, a numerical test on its validity by comparing to nonlocal calculations has not been carried out. The present study shows by means of model calculations that Penning ionization can very well be treated within the local theory. It turns out that the coupling to the Rydberg family A+B* is vital for the validity of the local ansatz in situations where the electron energy spectrum extends to small or even zero energy. This finding shows that for practical calculations Penning ionization differs from the related process of collisional detachment even though the formal theory can be written down the same way.