The high resolution Gas Phase Photoemission beamline, Elettra

Abstract The Gas Phase Photoemission beamlineat Elettra has been commissioned with outstanding success. All photoabsorption spectra taken between 90 and 900 eV have shown resolution which is equal to or higher than any published spectra. The monochromatoris a variable angle spherical grating instrument ( plane mirrorand grating between entrance and exit slits), with an undulator as the source. Some of the problems encountered in commissioning and their solutions are discussed. In particular the calibration is complicated by the fact that an infinite number of angle pairs of the mirror and grating exist for a particular photon energy, whereas only one angle pair gives the highest resolution. A second problem is that the resolution is so high that above about 80 eV, it is much smaller than the lifetime broadening of any known absorption resonance, making any determination of resolution difficult. The experimental chambers available for users are described together with some examples of spectra which have been taken.