Photoionization cross sections and photoelectron asymmetries of the valence orbitals of NO

Abstract

Partial photoionization cross sections and photoelectron asymmetry parameters were measured for the valence orbitals of NO over the photon energy range 16–31 eV by photoelectron spectroscopy, using synchrotron radiation. The results are compared with previous measurements and with theoretical curves based on the multiple-scattering model. Maxima observed in the partial cross sections of the 2π, 5σ, and 4σ orbitals are attributed to continuum shape resonances. The multiple-scattering model calculations predict the observed photoelectron asymmetries of the 5σ and 1π orbitals very well, but the calculated asymmetry curves are shifted strongly from the measured asymmetries produced by the 2π and 4σ orbitals. The π molecular orbitals are observed to produce qualitatively different photoelectron asymmetry curves than do the σ orbitals. We discuss the double-angle-time-of-flight method for the measurement of photoelectron angular distributions. This technique offers the advantages of increased electron collection efficiency and the elimination of certain systematic errors.