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This article reports on the high-resolution performance of the grazing-incidence plane grating monochromator SX700/II, installed at BESSY by the Freie Universität Berlin, in the photon energy range from about 40 to 900 eV. The high resolving power up to 10 000 achieved with this monochromator is based on improving the figure error of the ellipsoidal focusing mirror, on reducing the vertical dimension of the beam source, and on employing a 5-μm exit slit. We report on high-resolution gas-phase studies in the double-excitation region of He, as well as at core-excitation thresholds of Ne, Ar, Kr, and Xe in the photon-energy range from ≂45 eV to ≂900 eV. In addition, high-resolution core-excitation spectra at the K thresholds of C, N, and O are presented for gas-phase CO, N2, and O2. In all cases, high-n Rydberg states and/or vibrational sidebands of the electronic excitations were resolved. The various contributions to the present instrumental linewidths are discussed as well as the prospects for further improvements in resolution with this monochromator.

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During the last 10 years various types of soft x-ray monochromators have been developed, which are optically based on the plane grating focusing condition introduced in 1980. These instruments as well as those using the original 1980 optical configuration are reviewed and compared to the other type of high performance soft x-ray grating monochromator, the Rowland circle based spherical grating monochromator (SGM). Performance data of a plane grating monochromator (HE-PGM3), which was recently commissioned at BESSY and which offers a broad spectral range (40-2000 eV) and very high spectral resolution (up to EIAE-10 000) are given in more detail. The performance of grating and crystal monochromators is compared in the l-2 keV photon energy range.

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