title: Electron-Proton Decoupling in Excited-State Hydrogen Atom Transfer in the Gas Phase.
abstract: Hydrogen-release by photoexcitation, excited-state-hydrogen-transfer (ESHT), is one of the important photochemical processes that occur in aromatic acids and is responsible for photoprotection of biomolecules. The mechanism is described by conversion of the initial state to a charge-separated state along the O(N)-H bond elongation, leading to dissociation. Thus ESHT is not a simple H-atom transfer in which a proton and a 1s electron move together. Here we show that the electron-transfer and the proton-motion are decoupled in gas-phase ESHT. We monitor electron and proton transfer independently by picosecond time-resolved near-infrared and infrared spectroscopy for isolated phenol-(ammonia)5 , a benchmark molecular cluster. Electron transfer from phenol to ammonia occurred in less than 3 picoseconds, while the overall H-atom transfer took 15 picoseconds. The observed electron-proton decoupling will allow for a deeper understanding and control of of photochemistry in biomolecules.
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-15, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan).
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Miyazaki
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-15, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan).
authors.forename: Ryuhei
authors.initials: R
authors.lastname: Ohara
authors.affiliation: Division of Chemistry, Center for Natural Sciences, College of Liberal Arts and Sciences, Kitasato University, 1-15-1 Kitazato, Sagamihara, Kanagawa 228-8555 (Japan).
authors.forename: Kota
authors.initials: K
authors.lastname: Daigoku
authors.affiliation: Department of Chemistry, Tokyo Metropolitan University, Minami-Osawa, Hachioji, Tokyo 192-0397 (Japan).
authors.forename: Kenro
authors.initials: K
authors.lastname: Hashimoto
authors.affiliation: Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo, 153-8902 (Japan).
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Woodward
authors.affiliation: CNRS, Aix Marseille Université, Physique des Interactions Ioniques et Moleculaires (PIIM) UMR 7345, 13397 Marseille cedex (France).
authors.forename: Claude
authors.initials: C
authors.lastname: Dedonder
authors.affiliation: CNRS, Aix Marseille Université, Physique des Interactions Ioniques et Moleculaires (PIIM) UMR 7345, 13397 Marseille cedex (France). christophe.jouvet@univ-amu.fr.
authors.forename: Christophe
authors.initials: C
authors.lastname: Jouvet
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-15, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan). mfujii@res.titech.ac.jp.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Fujii
keywords: IR spectroscopy; hydrogen transfer; photochemistry; reaction mechanisms; time-resolved spectroscopy