Destruction of Metastable Helium Atoms in Binary Collisions

A calculation of the cross section for the reaction He′+He′=He+He++e (destruction of the metastable 23S state by ionization) has been performed by means of the perturbed stationary state method. The cross section obtained is of the order of magnitude 10—18 cm2 at room temperature and increases slowly with decreasing kinetic energy of the colliding particles. The magnitude of the cross section fits well with a tentative scheme which considers processes of the type A′+B=A+B++e as being intermediate between true resonance collisions and nonresonance collisions. It disagrees by 4 orders of magnitude with experimental findings [A. V. Phelps and J. P. Molnar, Phys. Rev. 89, 1202 (1953)]. The reason for this discrepancy is not known.