Stability, Electronic Structure and Vibrational Modes of Ti_8C_12 Dimer

We present our density functional results of the geometry, electronic structure and dissociation energy of Ti_8C_12 dimer. We show that as opposed to the currently held view that Ti_8C_12 are highly stable monodispersed clusters, the neutral Ti_8C_12 clusters form covalent bonds and form stable dimers. We determine that the Ti atoms bond weakly (0.9 eV/bond) to organic ligands such as ammonia. Alternatively the Met-Car dimer has a cohesive energy of 4.84 eV or approximately 1.2 eV per bond. While Met-Car dimers are stable, formation of these dimers may be quenched in an environment that contains a significant population of organic ligands. The ionization and dissociation energies of the dimer are of same order which prevents the observation of the dimer in the ion mass spectroscopy. The analysis of the vibrational frequencies show the lowest-energy structure to be dynamically stable. We also present infrared absorption and Raman scattering spectra of the Ti_8C_12 dimer.Comment: 5 pages, 3 figures (Better quality figures available on request). Physical Review B (Rapid Communication) (2002, in press

Heliostat mirror survey and analysis

The mirrors used on concentrating solar systems must be able to withstand severe and sustained environmental stresses for long periods of time if they are to be economically acceptable. Little is known about how commercially produced wet process silvered second surface mirrors will withstand the test of time in solar applications. Field experience in existing systems has shown that the performance of the reflective surface varies greatly with time and is influenced to a large extent by the construction details of the mirror module. Degradation of the reflective layer has been seen that ranges from non-observable to severe. The exact mechanisms involved in the degradation process are not well understood from either the phenomenological or microanalytical points of view and are thus subject to much debate. The three chapters of this report summarize the work recently performed in three general areas that are key to understanding and ultimately controlling the degradation phenomena. These areas are: a survey of the present commercial mirroring industry, the microanalytical examination of numerous degraded and nondegraded mirrors, and an investigation of several novel techniques that might be used to extend the life of heliostat mirrors. Appendices include: (a) list of mirror manufacturers and (b) recommended specifications for second surface silvered mirrors for central receiver heliostat applications. (WHK

Waste package environment studies. FY 1984 annual report.

Tests were conducted by Pacific Northwest Laboratory in FY 1984 to examine the influence of heat and radiation on the chemical environment of a high-level nuclear waste package in a repository in salt and to determine the solubility of key radionuclides in site-specific brines. These tests are part of an ongoing effort by the Waste Package Program, whose objective is to help develop a data base on package components and system interactions necessary to qualify a nuclear waste package for geologic disposal. Specifically, tests performed in FY 1984 involved alpha and gamma radiolysis of brines, americium solubility in brines, the influence of heat and radiation on rock salt, and the influence of temperature on brine chemistry