ELECTRON-IMPACT EXCITATION OF AUTOIONIZING LEVELS OF KR AND XE BETWEEN THE P-2(3 2) AND P-2(1/2) IONIC LIMITS/

We have observed electrons ejected from autoionizing levels which lie between the P-2(3/2) and P-2(1/2) ionic limits for Kr and Xe. Kinetic energy spectra of the ejected electrons were obtained following electr on-impact excitation of the target gases by using time-of-flight spect roscopy in a crossed-beam experiment. Spectral features which correspo nd to electrons ejected from both odd and even parity autoionizing lev els have been identified. Some of the features have kinetic energies o f just over 0.1 eV and have been resolved for the first time in an ele ctron-impact experiment. The most intense features at low electron-imp act energies come from optically forbidden np' and nd' terms. It was p ossible to estimate the integral cross section for autoionization by c omparing the intensity of the elastically scattered electrons with the intensity of the autoionizing features. For Xe, autoionization from t he levels which lie between the ionic limits appears to account for ab out 67% and 7.6% of the electron-impact ionization cross section at im pact energies of 14 and 24 eV, respectively; while for Kr, the fractio ns are 20% and 2.7% at 16 and 26 eV.