Generalized Oscillator Strength for 11S→21P Transition of Helium. Theory of Limiting Oscillator Strengths

Abstract

Relative generalized oscillator strengths have been determined for the $1^1{\text{S→2}}^{1}P$ transition in helium as a function of momentum change of the colliding electron and normalized to the theoretical oscillator strength {calculated by Schiff and Pekeris [Phys. Rev. 134, A638 (1964) ]} at zero momentum change. The validity of the normalizing procedure is investigated theoretically and it is shown that the limit of the generalized oscillator strength at zero momentum change is equal to the optical oscillator strength for any atom or molecule at any incident energy regardless of whether the first Born approximation holds. The normalizing procedure is therefore justified. The results are compared with the experimental and theoretical oscillator strengths obtained by other investigators. The limiting relation for oscillator strengths is established under much more general conditions than in any previous research.