Electron impact excitation of autoionizing levels of Kr and Xe between the and ionic limits

Abstract

We have observed electrons ejected from autoionizing levels which lie between the and ionic limits for Kr and Xe. Kinetic energy spectra of the ejected electrons were obtained following electron-impact excitation of the target gases by using time-of-flight spectroscopy in a crossed-beam experiment. Spectral features which correspond to electrons ejected from both odd and even parity autoionizing levels have been identified. Some of the features have kinetic energies of just over 0.1 eV and have been resolved for the first time in an electron-impact experiment. The most intense features at low electron-impact energies come from optically forbidden np' and n' terms. It was possible to estimate the integral cross section for autoionization by comparing the intensity of the elastically scattered electrons with the intensity of the autoionizing features. For Xe, autoionization from the levels which lie between the ionic limits appears to account for about 67% and 7.6% of the electron-impact ionization cross section at impact energies of 14 and 24 eV, respectively; while for Kr, the fractions are 20% and 2.7% at 16 and 26 eV.