Oriented molecule photoelectron angular distributions in the vicinity of a photoionization shape resonance: Continuum multiple scattering-X alpha calculations for valence ionization of CF3Cl

The potential use of fixed molecule photoelectron angular distributions (PADs) as a detailed probe of photoionization dynamics is explored using Continuum Multiple Scattering-X alpha calculations for the molecule CF3Cl. A number of dynamical phenomena (various shape resonances and a Cooper minimum) encountered in the vuv photoionization of CF3Cl up to 70 eV are examined. Cross-sections and asymmetry parameters are also reported and the nature of the low energy shape resonances is examined using eigenchannel plots. These show a clear correspondence between the present scattering calculations and the alternative description of shape resonances as antibonding virtual valence orbitals. PADs from fixed in space molecules are predicted to show a pronounced orientation, favoring electron emission from one end of the molecule. After passing through a shape resonance this orientation can flip direction as a consequence of resonant phase shifts in the interfering partial waves. Resonant electron-ion interactions can also result in greater alignment of the electron's orbital angular momentum with the molecular axis; the corollary is that the PAD becomes less strongly aligned or oriented along this direction at the resonance energy. (C) 1997 American Institute of Physics.