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The vapor-liquid phase behavior and the critical behavior of the square-well (SW) fluid are investigated as a function of the interaction range, λ∈ [1.25, 3], by means of the self-consistent Ornstein-Zernike approximation (SCOZA) and analytical equations of state based on a perturbation theory [A. L. Benavides and F. del Rio, Mol. Phys. 68, 983 (1989); A. Gil-Villegas, F. del Rio, and A. L. Benavides, Fluid Phase Equilib. 119, 97 (1996)]. For this purpose the SCOZA, which has been restricted up to now to a few model systems, has been generalized to hard-core systems with arbitrary interaction potentials requiring a fully numerical solution of an integro-partial differential equation. Both approaches, in general, describe well the liquid-vapor phase diagram of the square-well fluid when compared with simulation data. SCOZA yields very precise predictions for the coexistence curves in the case of long ranged SW interaction (λ>1.5), and the perturbation theory is able to predict the binodal curves and the saturated pressures, for all interaction ranges considered if one stays away from the critical region. In all cases, the SCOZA gives very good predictions for the critical temperatures and the critical pressures, while the perturbation theory approach tends to slightly overestimate these quantities. Furthermore, we propose analytical expressions for the critical temperatures and pressures as a function of the square-well range. [ABSTRACT FROM AUTHOR]

Theoretical studies on the GenCm (n=1,2; m=1–3) microclusters have been performed using the state of the art calculations. Several alternative structures of these clusters were studied to locate the lowest-energy isomers. It is observed that the structures of the complexes result from the competition between ionic Ge–C, conjugated covalent C–C, and metallic Ge–Ge bonds. The ionization of the molecules enhances the ionic character of the Ge–C bond and has significant structural consequences. Using theoretically determined partition functions, thermodynamic data are computed and experimental enthalpies are enhanced. The ab initio atomization energies of germanium carbides compare well with corrected experimental functions. The experimental appearance potentials are well reproduced by the theoretical ionization potentials. [ABSTRACT FROM AUTHOR]

Energy- and charge-transfer processes in neon-hydrogen mixtures (500–1400 hPa neon and 0.001–3 hPa hydrogen partial pressures) excited by a pulsed low-energy (∼10 keV) electron beam were investigated using time-resolved spectroscopy. Time spectra of the hydrogen Lyman-α line, neon excimer emission (second continuum), and neon atomic lines (3p–3s transitions) were recorded. The time-integrated intensity of the Lyman-α emission was measured for the same range of gas mixtures. It is shown that direct energy transfer from Ne2* excimers and neon atoms in the four lowest excited states as well as recombination of H3+ ions are the main channels populating atomic hydrogen in the n=2 state. A rate constant of (4.2±1.4)×10-11 cm3 s-1 was obtained for the charge transfer from Ne2+ ions to molecular hydrogen. A lower limit for the depopulation rate constant of Ne2* excimers by molecular hydrogen (combination of energy transfer and ionization) was found to be 1.0×10-10 cm3 s-1. [ABSTRACT FROM AUTHOR]

The inner-shell C 1s photoionization of randomly oriented molecules of the chiral compound carvone has been investigated using circularly polarized synchrotron radiation up to 30 eV above threshold. Binding energies of the C_==O and C_H2== carbon 1s orbitals were determined to be 292.8±0.2 and 289.8±0.2 eV, respectively. The remaining C_–H C 1s levels substantially overlap under an intense central peak centered at 290.5±0.2 eV. The angle-resolved photoemission from the carbonyl carbon C_==O core orbital in pure carvone enantiomers shows a pronounced circular dichroism of ∼6% at the magic angle of 54.7° to the light beam propagation direction. This corresponds to an expected 0°–180° forward-backward electron emission asymmetry of ∼10%. On changing between the R and S enantiomers of carvone the sense or sign of the asymmetry and associated dichroism effectively reverses. The observed circular dichroism, and its energy dependence, is well accounted for by calculations performed in the pure electric dipole approximation. [ABSTRACT FROM AUTHOR]