Infrared spectroscopy of resonantly ionized (Phenol)(H2O)(n)(+)

The infrared spectra of (phenol)(H2O)(n)(+) cluster ions (n = 1-4, 7, 8) ha ve been recorded in the region from 2850 to 3800 cm(-1). The method develop ed for this study (IR-PARI = infrared photodissociation after resonant ioni zation) allows sensitive IR spectroscopy of cluster ions from size-selected neutral precursors. The three-color laser scheme used for ion selection an d dissociation consists of a two-color S-0 --> S-1 --> D-0 ionization of a mass-selected cluster followed by IR photodissociation of the cluster ion. The IR spectra were taken by monitoring the photodissociation dip of the pa rent ion signal and by recording the rise of the -H2O fragment signal. The experimentally observed frequencies are compared to the results of ab initi o calculations. No proton transfer is observed for the (phenol)(H2O)(1,2)() clusters. In contrast to the S-0 state, the structure of (phenol)(H2O)(2) (+) turns out to be linear. In the case of the (phenol)(H2O)(3,4)(+) cluste rs, linear and solvated structures are discussed. Within the solvated struc tures, proton transfer can occur between phenol and the water molecule, whi ch is hydrogen-bonded to phenol. The observed fragmentation thresholds indi cate proton transfer for (phenol)(H2O)(n greater than or equal to 4)(+) on the nanosecond time scale of pur experiment. At least for the (phenol)(H2O) (8)(+) cluster, the second solvation shell is full and a third solvation sh ell will be formed.