Experiments in Weak Acid Dissociation and Theories of Activated Rate Processes.

Activated chemical reactions in condensed media constitute the most important type of chemistry near the earth's surface. With the help and intuition provided by the successes of gas phase chemistry, two technological advances, subpicosecond time-resolved spectroscopy and theoretical calculations using super computers, have brought the goal of a molecular level understanding in condensed phase chemistry closer to view. In the experimental studies, lifetime and quantum yield measurements were performed on the excited states of 1-naphthol-2-sulfonic acid potassium salt (1-ROH-2-S) and its associated anion in aqueous solutions. In comparison to 1-naphthol, the intramolecular hydrogen bonding in the sulfonate derivative sterically reduces the extramolecular proton dissociation and recombination rates. Despite the large differences between excited state rates in 1-ROH -2-S and those in 1- and 2-naphthol, proton dissociation in all these molecules is controlled by reorientational motions of the adjacent water and requires a special (H _2O)_{4+/- 1} cluster as the proton acceptor. These findings support the Robinson-Lee-Moore hydration model for proton dissociation in aqueous environments. In the theoretical studies, two generalized theories of activated chemical reactions were developed using space-dependent friction. One method used the Carmeli-Nitzan approach, which is based on a Langevin equation. The second method employed the recent theory of Pollak-Grabert-Hanggi based on a Hamiltonian approach. The latter theory gave rise to interesting scaling properties in certain limits.