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The liquid-vapor interface of a bismuth-gallium mixture (0.2 percent bismuth and 99.8 percent gallium) at 36 degrees C has been studied by grazing incidence x-ray diffraction. The data show, in agreement with thermodynamic arguments, that bismuth is heavily concentrated in the liquid-vapor interface. The x-ray diffraction data are interpreted with the assistance of a simple model that represents the interface as a partial monolayer of bismuth. This analysis leads to the conclusion that the bismuth concentration in the interface is about 80 percent, that there is no significant mixing of gallium and bismuth in the interface, and that the structure function of the interfacial bismuth is like that of supercooled bulk liquid bismuth.

High-resolution x-ray photoabsorption measurements on Ar near its K edge are reported. A number of new two-electron KM features were detected. The three-electron KM and the two-2 electron KL spectra were measured. The previously unresolved three-electron KM and the two-2 electron KL spectra were clearly resolved in this study. Identification of spectral features is discussed based on our Hartree-Fock and published Dirac-Fock [Dyall, J. Phys. B 16, 3137 (1983); Dyall and LaVilla, Phys. Rev. A 34, 5123 (1986)] energy-level calculations. PACS number(s): 32.80.Hd, 32.30. RjMultielectron processes in atoms depend sensitively on intra-atomic correlations and the dynamics of the excitation. They can provide, therefore, an insight into the electronic structure and the excitation process which goes beyond prevailing single-electron fixed-potential models.X-ray near-edge photoabsorption measurements in noble gases, which are free from extended x-ray-absorption finestructure (EXAFS) interference and probe the energies and cross sections directly, are particularly well suited for these studies. The near-K-edge spectra of neon [1], argon [2], krypton [3), and xenon [4] were measured with high resolution, showing a rich array of two-electron (2e) and even some three-electron (3e) excitations. In particular, the very detailed measurements of Deslattes et at.[2] on Ar were repeatedly used to test models for the excitation dynamics and the importance of effects, such as post-collisional interaction, exchange, ground-, and final-state correlations and relaxation [5 -8]. However, sharp features involving 2e ls3s and 3e 1s3lI' states could not be resolved in those synchrotron-radiation mes surements (underline denotes hole states). Furthermore, no ls2l features were reported to date for Ar, although such features were detected in Ne [1] and Kr [3]. We report here high-resolution measurements of the photoabsorption spectrum of Ar in the KM and KL regions.A number of previously unresolved 1s3p and ls3s features were detected, and the 3e KMz and 2e KL features were resolved. Tentative identification of these, based on our Hartree-Fock (HF) energy-only and published [9, 7] Dirac-Fock (DF) calculations, is also presented.The measurements were done at the EXAFS II mirrorfocused beamline at HASYLAB in a standard transmission EXAFS configuration, using an UHV-compatible double-crystal Si(111) monochromator. Harmonics were electively eliminated by detuning the monochromator crystals using a stabilization feedback control [10]. The fiux at the sample was~10 e photons/sec and the energy resolution LE-0.9 eV. Reference scans without sample were done to obtain absolute cross sections. Incident beam stability and measurements statistics were high 1.5 1.0-0.5-0 0 100 I 200 ENERGY (eV) 300 I 400 FIG. 1. Near-K-edge photoabsorption spectrum of Ar. Zero energy is at the edge, E~=3206.26 ev. enough to allow confident detection of features as small as 0,02pp of the K edge. The energy scale was established using the resonance line at [11] Ei, 4"--3203...