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The photoabsorption of LiF, LiCl, and LiBr has been investigated with high resolution at quantum energies from 60 to 230 eV using synchrotron radiation from an electron storage ring. It is found that the spectra can be understood largely in terms of transitions from the various core levels to the final-band density of states as obtained from recent band calculations. Features are found which may possibly be due to replication of the edge with the emission of one or more collective excitations. Substantial progress has recently been made toward a detailed understanding of the optical response of LiF, LiCl, and LiBr over a wide range of energies in the extreme ultraviolet. The lithium K shell provides especially suitable initial states because of large dipole matrix elements with the final band states and also the lack of strong resonances in the continuum beyond threshold. 1 Previous results on the lithium halides have been reported by Haensel, Kunz, and Sonntag in the spectral range 60-70 eV. 2 The present measurements extend some 150 eV higher in energy, and they provide values of absorption coefficient so that the importance of transitions from the various core states, for example, the Li + K, the Cl~ L n>m , the Br" M IVt v? and the Br"" M n>in can be assessed. Moreover, it has recently been possible to carry out a self-consistent Hartree-Fock energy-band calculation including the principal polarization or many-body corrections for LiCl 3 and also for LiBr. 4 This permits the comparison of theoretical and experimental optical spectra so as to determine the importance of core excitons and multiple excitations.The absorption coefficients were determined by observing the transmission of thin films of various thicknesses evaporated in situ onto thin Formvar substrates. Film thicknesses were determined by a quartz crystal monitor calibrated by the Tolansky technique. The synchrotron continuum from the 240-MeV electron storage ring at the University of Wisconsin Physical Science Laboratory was used as a light source. Radiation transmitted by the substrates (and by the substrates plus samples) was dispersed by a 2m grazing-incidence spectrometer with 10-/Lim entrance slits and a 576-line/mm grating. Digital recording of the photon counting rate as well as monitor and wavelength information was employed during scans of about 30 min each. When structure appeared it was possible to slow down the scanning rate so as to include many more points in the same wavelength interval. Scans were repeated and later combined during the computer analysis. The data reduction techniques, methods for filtering out stray light, etc., are described elsewhere. 5 Absolute absorption coefficients were determined to 30% accuracy and the wavelength resolution was 0.1 A. Measurements were made with the film at room temperature since little narrowing of the observed structure occurred upon cooling to 77°K. Figure 1 shows the experimental results for the three materials over a wide spectral range. The absorption coefficients a (cm"" 1 ) are plot...

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The 240 MeV storage ring at the Physical Science Laboratory of the University of Wisconsin has been used as a source of radiation for extreme uv spectroscopy in the 40–400 Å wavelength range. The characteristics of the synchrotron radiation emitted by this machine are summarized. The experimental setup with a 2 m grazing spectrometer and the data acquisition system is described along with some of the procedures used for thin film photoabsorption measurements.