			15min:

VIBRATIONAL PREDISSOCIATION SPECTROSCOPY OF THE (H₂O)_n^- n=6-21 CLUSTERS IN THE OH STRETCHING REGION: EVOLUTION OF THE EXCESS ELECTRON-BINDING SIGNATURE INTO THE INTERMEDIATE CLUSTER SIZE REGIME.

JOSEPH C. BOPP, JOSEPH R. ROSCIOLI, NATHAN I. HAMMER, MARK A. JOHNSON, Sterling Chemistry Laboratory, Yale University, PO Box 208107, New Haven, CT 06520.

We report vibrational predissociation spectra of the (H₂O)_n^- cluster ions in the OH stretching region to determine whether the spectral signature of the electron-binding motif identified in the smaller clusters continues to be important in the intermediate size regime (n=7-21). This signature consists of a redshifted doublet that dominates the OH stretching region, and has been traced primarily to the excitation of a single water molecule residing in a double H-bond acceptor (AA) binding site, oriented with both of its H atoms pointing toward the excess electron cloud. Strong absorption near the characteristic AA doublet is found to persist in the spectra of the larger clusters, but the pattern evolves into a broadened triplet around n=11. A single free OH feature associated with dangling hydrogen atoms on the cluster surface is observed to emerge for n=15, in sharp contrast to the multiplet pattern of unbonded OH stretches displayed by the H⁺ cdot (H₂O)_n clusters throughout the n=2-29 range.