title: Probing the threshold to H atom transfer along a hydrogen-bonded ammonia wire.
abstract: We characterized the entrance channel, reaction threshold, and mechanism of an excited-state H atom transfer reaction along a unidirectionally hydrogen-bonded "wire" -O-H...NH3...NH3...NH3...N. Excitation of supersonically cooled 7-hydroxyquinoline.(NH3)3 to its vibrationless S1 state produces no reaction, whereas excitation of ammonia-wire vibrations induces H atom transfer with a reaction threshold approximately 200 wave numbers. Further translocation steps along the wire produce the S1 state 7-ketoquinoline.(NH3)3 tautomer. Ab initio calculations show that proton and electron movement along the wire are closely coupled. The rate-controlling S1 state barriers arise from crossings of a pipi* with a Rydberg-type pisigma* state.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Tanner
authors.forename: Carine
authors.initials: C
authors.lastname: Manca
authors.forename: Samuel
authors.initials: S
authors.lastname: Leutwyler