The gas-phase photoemission beamline at Elettra

This paper reports the present stage of commissioning of the gasphase photoemission beamline at Elettra, Trieste. The beamline is designed for atomic and molecular science experiments with highresolution and high-¯ux synchrotron radiation. It consists of an undulator source, variable-angle spherical-grating monochromator and two experimental stations. The design value of the energy range is 20 to 800 eV with a speci®ed resolving power of over 10000. The procedure adopted for calibration of this type of monochromator is discussed. At present a resolving power up to 20000 and a range up to 900 eV have been measured. Absorption spectra taken at the argon LII,III-edge and at the nitrogen, oxygen and neon K-edges are as sharp as, or sharper than, any reported in the literature. The instrumental broadening is well below the natural line-width making it dif®cult to quantify the resolution; this problem is discussed.