Infrared photodissociation spectra of [aniline-(H 2 O) n ] + (n = 1-8) are measured in the 2700-3800 cm-1 region. The spectra are interpreted with the aid of density functional theory calculations. The n = 1 ion has an N-H•••O hydrogen bond. The spectrum of the n = 2 ion demonstrates a large perturbation to both of the NH oscillators, indicating the 1-1 structure where each NH bond is bound to a water molecule. For the n = 3 ion, the calculated spectrum of the 2-1 branched structure coincides well with the observed one. For the n = 4 ion, there exist three strong bands at 2960, 3100, and 3430 cm-1 , and a very weak one at 3550 cm-1. The observed spectrum in the 3600-3800 cm-1 region is decomposed into four bands centered at 3640, 3698, 3710, and 3734 cm-1. The 2-2 branched isomer is responsible for all the features except the 3550 and 3710 cm-1 bands. These two bands are due to another isomer with a five-membered ring. An infrared band characteristic of the n = 5 ion appears at 3684 cm-1 , which is not seen in the spectra of the n = 1-4 ions. This band is indicative of a ring structure and assigned to the free OH stretching vibration of the three-coordinated (double-acceptor-single-donor

Infrared photodissociation spectra of the aniline ion solvated by water and methanol molecules are measured in the 2600-3800 cm-1 region. Substantially red-shifted and broadened transitions are distinctly observed at 3105 and 2915 cm-1 for aniline +-(H 2 O) 1 and aniline +-(CH 3 OH) 1 , respectively, and assigned to the stretching vibration of the hydrogenbonded NH oscillator of the aniline + moiety. The spectra of aniline +-(H 2 O) 2 and aniline +-(CH 3 OH) 2 demonstrate a large perturbation to both of the NH oscillators, indicating that each NH bond is bound to a solvent molecule in the most stable structure.

Vibrational spectra of hetero-dimer and trimer ions containing aniline + are measured by infrared photodissociation spectroscopy. For the dimer ions, the NH 2 bending overto ne band gains its intensity through Fermi resonance interaction with the hydrogen-bonded NH stretching fundamental. Unperturbed frequencies of the NH 2 bending overtone are ca lculated to be in the range of 3255-3276 cm-1 , suggesting that the frequency is almost inta ct upon cluster formation. For the trimer ions, Fermi resonance interaction occurs mainly between the NH 2 bending overtone and the stretching fundamental of the NH oscillator in volved in the stronger hydrogen bond.

The intracluster proton transfer in aniline-amine complex ions is investigated by infrared photodissociation spectroscopy and density functional theory calculations. The p roton acceptors include ammonia, methylamine, dimethylamine and trimethylamine in asce nding order of proton affinity. The spectra of (aniline-ammonia) + and (aniline-methylami ne) + demonstrate the persistence of the aniline ion unit in the complexes. For (aniline-di methylamine) + and (aniline-trimethylamine) + , the spectra imply the transformation to the a nilino radical (C 6 H 5 NH) unit, suggesting the occurrence of the proton transfer.

Infrared photodissociation spectra of aniline +-M (M = thiophene, furan and phenol) are measured in the 2700-3700 cm-1 region and analyzed by density functional theory calculations. Only a structure with a π-type hydrogen bond is found for aniline +-thiophene. Two structural isomers are identified for aniline +-furan and aniline +-phenol, which have either a π-type or a σ-type hydrogen bond, where an amino proton of aniline + interacts with the π-electrons or the oxygen atom of the neutral molecules, respectively. The isomer with a σ-type hydrogen bond is more stable for aniline +-phenol, while less stable for aniline +-furan.