Electronic and geometric structure of acetylide carbon on the surface of lithium

The reaction products formed on clean evaporated lithium films exposed to acetylene gas under UHV conditions were examined with ultraviolet photoelectron and Auger electron spectroscopies. Good agreement was obtained between the observed ultraviolet photoelectron spectrum and a spectrum simulated from ab initio calculations for C₂Li₂ in D_2h symmetry. The components of the C(KW) Auger signal were also consistent with carbon being present as C₂^n? units (acetylide) rather than as carbonaceous aggregates or as monomeric carbon. The observed carbon AES structure was fit in good agreement by a simulation using experimental electronic binding energies and Auger transition intensities calculated for C₂Li₂. Saturation of the ultraviolet and Auger electron signals with increasing exposure to HC₂H was not found, although thin films of lithium were slowly consumed on long exposure to acetylene. A loss of the reaction product from the interfacial region was indicated. Cluster models of acetylide on the (100) face of lithium, C₂/Li₈(6, 2)-(100), were used to investigate geometric arrangement of C₂^n? relative to lithium. The results show that acetylide resident in the interface below the first layer of lithiums of the model was energetically favored compared to C₂^n? resident on top of the first layer of lithium. The stability of this conformation was calculated to be further increased by a small expansion of lithiums near neighbor to C₂Li₂. The restructuring calculated for the model complements the absent saturation and suggests that C₂^n? units diffuse into the actual film via a local expansion.     

A disorder parameter that test for confinement in gauge theories with quark fields

We propose to use a suitably defined vortex free energy as a disorder parameter in gauge field theories with matter fields. It is supposed to distinguish between the confinement phase, massless phase(s) and Higgs phase where they exist. The matter fields may transform according to an arbitrary representation of the gauge group. We compute the vortex free energy by series expansion for a Z₂ Higgs model and for SU(2) lattice models with quark or Higgs fields in the fundamental representation at strong coupling (confinement phase), and for the Z₂ Higgs model in the range of validity of low-temperature expansions (Higgs phase). The results are in agreement with the expected behavior.     

Calculation of electron-transfer rate constants from intervalence transfer absorption bands

Rates of intramolecular electron transfer are calculated from the properties of intervalence transfer absorption bands for a series of mixed-valence ruthenium dimers. The calculations are based on theoretical results obtained by Duke, Hopfield, and others, and are shown to be in agreement with earlier results obtained from outer-sphere electron transfer rate constant measurements.