In this contribution, studies of the dynamics of proton-transfer reactions in solvent cages are presented, building on earlier work [Breen, J. J.; et al. J. Chem. Phys. 1990, 92, 805. Kim, S . K.; et al. Chem. Phys. Lett. 1994, 228, 3691. The acid-base system studied in a molecular beam is 1-naphthol as a solute and ammonia, piperidine, or water as the solvent, with the number of solvent molecules (n) varying. The rates and threshold for proton transfer have been found to be critically dependent on the number and type of solvent molecules: n = 2 for piperidine and n = 3 for ammonia; no proton transfer was observed for water up to n = 21. With subpicosecond time resolution, we observe a biexponential transient for the n = 3 cluster with ammonia.From these observations and the high accuracy of the fits, we provide the rate of the proton transfer at short times and the solvent reorganization at longer times. From studies of the effect of the total energy, the isotope substitution, and the number and type of solvent molecules, we discuss the nature of the transfer and the interplay between the local structure of the base solvent and the dynamics. The effective shape of the potential energy surface is discussed by considering the anharmonicity of the reactant states and the Coulombic interaction of ion-pair product states. Tunneling is related to the nature of the potential and to measurements specific to the isotope effect and energy dependence. Finally, we discuss a simple model for the reaction in finite-sized clusters, which takes into account the proton affinity and the dielectric shielding of the solvent introduced by the local structure.

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This paper presents a systematic study of gas-phase p-(7V,7V-dimethylamino)benzonitrile (DMABN) both in a supersonic jet expansion and in a thermalized vapor. From the jet studies, the excitedand ground-state vibrational spectra of the isolated molecule are resolved, and the spectroscopy of the stoichiometric complex with water, methanol, ammonia, and acetonitrile in the beam is reported. It is concluded that 1:1 complexes are not sufficient for the local perturbation to cause charge separation. At higher temperatures in the jet, we observe emission that we attribute to DMABN self-complexes. Under high pressure and temperature vapor conditions (>30 mTorr, 60 °C), red-shifted fluorescence from DMABN is observed. This is attributed to the charge-transfer state of DMABN in self-complexes.* Recipient of an Earl C. Anthony Fellowship.Contribution No. 7562. exists for a given charge-transfer or proton-transfer process. It is conceivable in the case of DMABN that a 1:1 DMABN/solvent complex could provide sufficient stabilization by charge-transfer or dipolar interactions to permit the photoisomerization of DMABN to its twisted charge-transfer state.27"30

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