High-resolution gas-phase photoelectron spectra using synchrotron radiation: Xe 4dlinewidths and the 4d5/2:4d3/2branching ratio

The performance of our new gas-phase photoelectron spectrometer and the Canadian Synchrotron Radiation Facility beamline at the Synchrotron Radiation Center (Stoughton, Wisconsin) is demonstrated with use of Xe 4d photoelectron spectra. The beamline employs a Grasshopper monochromator with a 1° grazing angle on the M1 mirror, and the Leybold-Heraeus combined lens-analyzer system is mounted at the magic angle to eliminate polarization and β effects. Both the photon and electron resolutions are very close to theoretical, and we have obtained Xe 4$d_{5/2}$ spectra with total widths as small as 0.262 eV at 94 eV photon energies. We have measured accurately and computer fitted the Xe 4$d_{5/2}$:4$d_{3/2}$ branching ratio from 74 to 150 eV photon energies. There is good qualitative agreement between our measured values and the latest theoretical relativistic random-phase-approximation values. Possible reasons for quantitative differences between theory and experiment are discussed.