Anomalous intensities in zero-kinetic-energy spectra

A number of reasons for the appearance of anomalous intensities in zero-kin etic-energy (ZEKE) spectroscopy are briefly reviewed and extended. Particul ar attention is paid to a recent paper of Matsui, Behm, and Grant in which the authors detect, in the ZEKE spectrum of NO2, a number of Franck-Condon forbidden transitions of significant intensity which they attribute in larg e part to channel interaction between allowed continua and Franck-Condon fo rbidden discrete Rydberg series. A quantitative approximate analysis of the ir data is given here which supports this claim. Implications of these resu lts for final state interactions in photoelectron spectroscopy are discusse d.