Damien Laage (a), Hagop Demirdjian (a) and James T. Hynes (a,b)
We will discuss the present status of our theoretical and computational work addressed to the question of whether a quantum of vibrational energy can be retained in a hydrogen stretching mode sufficiently long to induce, by infrared excitation, an acid-base proton transfer reaction in solution, schematically AH + B A- + HB+, where AH is the acid and B is the base. Ordinarily, one would view the solvent exclusively as a source of thwarting such a selective process, i.e. causing vibrational de-excitation of the excited H stretch before the excess energy could induce the reaction to occur; vibrational de-excitation can be quite rapid in hydrogen-bonded liquids of main interest as solvents for proton transfer reactions [1]. A non-traditional view of proton transfer reactions indicates, however, that the solvent can actually assist the IR-induced reaction [2]. After reviewing the concepts involved and initial calculations supporting them, we will discuss recent results [3,4] addressed to the efficacy of competing processes which could 'short-circuit' the desired reaction, focussing on the model system of hydrofluoric acid (HF) in water [5].
(b) Dept. of Chemistry and Biochemistry University of Colorado Boulder, CO 80309-0215 USA
References
[1] R. Rey, K. B. Moller and J.T. Hynes, « Ultrafast Vibrational Population Dynamics of Water and Related Systems : A Theoretical Perspective', Chem. Rev., 104, 1915-1928 (2004).
[2] H. J. Kim, A. Staib, and J. T. Hynes, `Ultrafast Dynamics at the Transition State inSolution', Ultrafast Reaction Dynamics at Atomic-Scale Resolution Femtochemistry and Femtobiology, Nobel Symposium 101, Villy Sundstrom, Ed., (Imperial College Press, London, 1998) pp. 510-527.
[3] D. Laage and J.T. Hynes, unpublished.
[4] H. Demirdjian, These, ENS-Paris VI (2004).
[5] K. Ando and J.T. Hynes, "Acid Ionization of HF in Water, an Electronic Structure and Monte Carlo Study", J. Phys. Chem. A, 103, 10398-10408 (1999).