The surface plasmon polariton-enhanced Raman spectra of size-selected C 16 , C 18 , and C 20 clusters isolated in nitrogen matrices are presented along with the calculated vibrational frequencies for the ring and linear chain isomers. The Raman spectra, recorded at a range of excitation wavelengths from 457.9 to 670 nm, show strong resonance enhancement for the three clusters. The calculated vibrational frequencies for ring and linear chain isomers and the cage and bowl structures for C 20 are compared to the experimental frequencies. Systematic shifts in the series of peaks in the 200 cm Ϫ1 region for C 16 , C 18 , and C 20 suggest that the observed isomers have the same geometry, thereby ruling out the bowl and cage isomers for C 20 . The measured spectra appear to be most consistent with the linear chain isomer. This high-energy isomer may be produced during neutralization of the deposited cluster ions.

A novel laser photolysis source has been used to synthesize hydrogen-terminated silicon clusters Si n H x + , where n e 50. Using mass spectrometry, the hydrogen content of the Si n H x + clusters with n ) 10-30 was measured as a function of temperature from 300 to 950 K. For n ) 10-22 at the lower temperatures, there is a broad distribution of [H]/[Si] ratios which peak around compositions expected for clusters with bulklike silicon cores (x/n > 1). Si n H x + clusters with x/n = 1 appear to be favored at intermediate temperatures. This stoichiometric composition suggests three-dimensional, Si n H n + cage-like structures built from Si-H units. The stability of the cage geometries is supported by density functional calculations. For cluster cations with n g 23 an abrupt transition occurs and there is a sharp drop in the hydrogen content at the lower temperatures. For these clusters, Si n H (n-y) + (y ) 1-5) compositions are prominent at the higher temperatures. These compositions suggest cage-like geometries with one or more internal silicon atoms. By adjusting the source conditions it is possible to generate Si n H x + (n g 23) clusters with a narrow distribution of x (less than two hydrogens wide).

The surface plasmon polariton-enhanced Raman spectra of size-selected, matrix-isolated C 14 neutral clusters are presented along with the calculated vibrational frequencies for the ring and linear chain isomers. The Raman spectra show resonance enhancement over a range of excitation wavelengths from 457.9 to 514.5 nm. The measured vibrational spectra are most consistent with the linear chain isomer. In addition, fluorescence spectra of neutral, mass-selected C n (n ) 14 and 18) clusters are presented. The isolated C 14 clusters display strong fluorescence with vibrational structure between 520 and 700 nm. The origins of the observed fluorescence for both C 14 and C 18 are investigated using the ZINDO/S, CIS, and TD-B3LYP methods.

Solubility equilibria are usually introduced in the general chemistry course with limited mention of the nonideal behavior of real solutions. Nonideal behavior is introduced in the qualitative analytical chemistry course in the context of gravimetry. Often this concept is left as an academic exercise with no experimental application. The determination of a solubility product constant as reported here differs from other experiments in that nonideality is taken into account through Debye-Hückel theory by making few simplifying assumptions.

No abstract