Infrared spectroscopic observation of the argon isomer distribution in evaporative ensembles of I-•ROH•Arm (R=methyl, ethyl, isopropyl) clusters

Vibrational predissociation spectra of argon-solvated iodide-alcohol clusters (I-. ROH . Ar-m, ROH=MeOH, EtOH, i-PrOH) are reported in the OH stretching region (3200-3400 cm-1). The spectra display multiple peaks associated with the ionic H-bonded OH stretching fundamental, which vary according to the extent of argon solvation. At small m, the number of peaks reflects the total number of attached argon atoms, such that peaks associated with fewer argons persist (with a small blue shift) in the spectra of the larger clusters, while new peaks appear red shifted by about 12 cm(-1) with each additional argon. The effect saturates in a manner that depends on the particular alcohol (m(max)=6 for MeOH, 5 for EtOH, and 4 for i-PrOH). We interpret these observations to indicate the presence of multiple isomers in the evaporative ensemble, which are distinguishable according to the different arrangements of argon atoms among two effective binding sites. (C) 1999 American Institute of Physics. [S0021-9606(99)01045-4].