title: Sequential proton transfer through water bridges in acid-base reactions.
abstract: The proton transfer mechanism between aqueous Brønsted acids and bases, forming an encounter pair, has been studied in real time with ultrafast infrared spectroscopy. The transient intermediacy of a hydrated proton, formed by ultrafast dissociation from an optically triggered photoacid proton donor ROH, is implicated by the appearance of an infrared absorption marker band before protonation of the base, B-. Thus, proton exchange between an acid and a base in aqueous solution is shown to proceed by a sequential, von Grotthuss-type, proton-hopping mechanism through water bridges. The spectra suggest a hydronium cation H3O+ structure for the intermediate, stabilized in the Eigen configuration in the ionic complex RO-...H3O+...B-.
authors.affiliation: Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
authors.forename: Omar F
authors.initials: OF
authors.lastname: Mohammed
authors.forename: Dina
authors.initials: D
authors.lastname: Pines
authors.forename: Jens
authors.initials: J
authors.lastname: Dreyer
authors.forename: Ehud
authors.initials: E
authors.lastname: Pines
authors.forename: Erik T J
authors.initials: ET
authors.lastname: Nibbering