title: Distance-dependent proton transfer along water wires connecting acid-base pairs.
abstract: We report time-resolved mid-IR kinetics for the ultrafast acid-base reaction between photoexcited 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS), and acetate at three concentrations (0.5, 1.0, and 2.0 M) and three temperatures (5, 30, and 65 degrees C) in liquid D(2)O. The observed proton-transfer kinetics agree quantitatively, over all times (200 fs-500 ps), with an extended Smoluchowski model which includes distance-dependent reactivity in the form of a Gaussian rate function, k(r). This distance dependence contrasts with the exponential k(r) that is typically observed for electron-transfer reactions. The width of k(r) is essentially the only parameter varied in fitting the proton-transfer kinetics at each concentration and temperature. We find that k(r) likely represents the rate of concerted (multi)proton hopping across "proton wires" of different length r that connect acid-base pairs in solution. The concerted nature of the proton transfer is supported by the fact that k(r) shows a steeper dependence on r at higher temperatures.
authors.affiliation: FOM-institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
authors.forename: M Jocelyn
authors.initials: MJ
authors.lastname: Cox
authors.forename: Rutger L A
authors.initials: RL
authors.lastname: Timmer
authors.forename: Huib J
authors.initials: HJ
authors.lastname: Bakker
authors.forename: Soohyung
authors.initials: S
authors.lastname: Park
authors.forename: Noam
authors.initials: N
authors.lastname: Agmon