Infrared predissociation of ternary cluster cations: the solvent effects on the branching ratio.

Infrared (IR) predissociation of hydrogen-bonded ternary cluster ions such as aniline-water-ethanol (AWE(+)), aniline-water-isopropanol (AWP(+)), aniline-methanol-ethanol (AME(+)), aniline-water-pyrrole (AWPy(+)), and aniline-water-benzene (AWB(+)) was examined in the region of 2700-4000 cm(-1) to explore the key factors which determine the branching ratios in the concurrent unimolecular dissociation. The smaller solvent molecule was predominantly ejected when the binding energies of the two were not too different. On the other hand, when they were far off, the binding energy also acted significantly on the branching ratio. Besides, mode-selective IR predissociation was observed, while the selectivity was not quite distinct. The IR predissociation of ternary cluster ions bound via hydrogen bonding is considered to occur on a time scale much faster than intramolecular vibrational energy redistribution, which was proved by a statistical transition state theory.