Mass-selected “matrix isolation” infrared spectroscopy of the I−·(H2O)2 complex: making and breaking the inter-water hydrogen-bond Original Research Article

Infrared spectra of the cold I−·W and I−·W2 clusters are reported via vibrational predissociation spectroscopy of the argon solvated species, I−·Wn·Arm, in the OH stretching region. Several argon atoms serve to significantly simplify the spectra by collapsing complex band contours into sharp features at the vibrational origins. This effect, in addition to the substantial cooling afforded by argon solvation, dramatically change the appearance of the bare dihydrate spectrum reported earlier [P. Ayotte, C.G. Bailey, G.H. Weddle, M.A. Johnson, J. Phys. Chem. A 102 (1998) 3067]. The cold spectrum consists of a simple four line pattern anticipated by ab initio calculations for the asymmetric structure where the two waters are bound together on one side of the ion. The dramatic changes in the spectrum of the argon complex relative to that of bare I−·W2 are readily interpreted to be a consequence of internal energy in the latter leading to rupture of the inter-solvent H-bond.