The solvation of the cesium ion by methanol has been investigated by gas-phase vibrational spectroscopy and Monte Carlo simulations of small ion clusters: Cs( CH 3 OH): , N = 4-25. The solvated ions, generated by thermionic emission and a molecular-beam source, have considerable amounts of internal energy. After excessive energy is dissipated by evaporation, quasistable cluster ions are mass-selected for vibrational predissociation spectroscopy using a line-tunable cw-C0 2 laser. Analysis of the vibrational spectra indicates that the first solvation shell about the cesium ion consists often methanol molecules. Larger Cs(CH 3 OH): (N) 18) appear to have small clusters of methanol bound to the surface of a solvated ion. Monte Carlo simulations using pairwise interaction potentials at 200, 250, and 300 K have been performed on Cs(CH 3 0H):, N = 6-16 and 25. The results from the simulations are consistent with the observed solvent shell size and suggest a significant role for hydrogen bonding in the larger solvated ions (N;;.lO). Once the first solvation shell is filled, the size of the solvent shell appears to be independent of the number of additional solvent molecules. Gas-phase solvated ions appear to be extremely useful models for dilute electrolyte solutions.

Cluster ions of the form Na + (CH 3 OH) N' N = 3-25 have been studied using experimental and theoretical methods. The cluster ions were prepared in a molecular beam by combining a thermionic alkali ion emitter with a continuous expansion of methanol in argon, and were found to contain a substantial amount of internal energy. A cw CO 2 laser was used to record the vibrational spectrum of mass-selected cluster ions in the 1020-1060 cm -I region. Information on the stepwise solvation of the sodium ion by methanol is gained by comparing changes in the spectra as a function of cluster size. The first solvation sphere of the sodium ion is occupied by six methanol molecules. Further solvent shell structure is seen for N> 6, including evidence of methanols resembling "bulk" solvent. The microscopic structure was investigated by Monte Carlo simulations of Na + (CH 3 OH) N' N =;= 6-24. Radial distribution functions display clear minima that indicate the spatial extent and occupation numbers of solvation shells. No hydrogen bonding takes place between methanol molecules in the first solvent shell but is instrumental in determining the framework of the rest of the cluster ion. The internal energies of the cluster ions were estimated using time-of-flight measurements and calculations within the evaporative ensemble formalism.

Dioxins and furans are believed to be among the most toxic chemicals known to man. The presence of these compounds in the emission gases of municipal solid waste incinerators and other combustion sources has raised debate over the location and the ultimate utility of incineration as an approach to waste management. Current methods used to measure dioxins and furans in combustion source emissions do not provide the real-time monitoring necessary to track average incinerator performance or upset emission levels. A study to design and develop a laser-induced fluorescence/continuous emission monitoring system to detect and quantify these compounds is being conducted. This paper reports the results of the study to date. Vapor-phase ultraviolet absorption spectra, absorption cross sections, and laser-induced fluorescence profiles are presented for three dioxins and two furans. These spectral data are needed for initial design and evaluation of the laser-induced fluorescence/continuous emission monitoring system approach.

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