Generalized oscillator strength studies for electron-impact 2s ionization of some low- and intermediate-Z atoms

Abstract

Generalized oscillator strengths (GOS) for ionization of the 2s subshell of several atoms are reported. The atomic wavefunctions used in the work have been obtained from a relativistic local density potential method known as the RC Xi E method. The GOS has been obtained using the Born approximation for 2s subshell ionization of Be, C, O, Ne, Al, Ar, Fe and Zn. The GOS behaviour has been studied both as a function of momentum transfer and energy transfer to understand the Bethe surface properties. Besides the RC Xi potential, the non-relativistic Hartree-Slater (HS) potential has also been used in a separate calculation for comparison. There is in general reasonably close agreement between the results of the RC Xi and the Ha calculations. The main feature of the GOS for 2s ionization is that in the case of small-Z atoms the GOS at threshold has its maximum at a finite value of K, away from the optical limit (K to O). At the position of the peak, significant contribution from optically forbidden partial wave channels has been observed. The 'Bethe ridge' is found to occur when delta approximately=(Ka0)2 at energies above the ionization threshold. At the ionization threshold itself, a ridge on the Bethe surface has been found to occur due to contributions from non-optical channels.