title: Proton/hydrogen-transfer coordinate of 2,5-dihydroxybenzoic acid investigated in a supersonic beam: combined IR/UV spectroscopy in the S0, S1, and D0 states.
abstract: As a model system for intramolecular proton/hydrogen-transfer coordinates, the structure of 2,5-dihydroxybenzoic acid is investigated for the ground, first electronically excited and also the ionic state. Combined IR/UV spectroscopy in molecular-beam experiments is applied and the experimental results are interpreted by the application of DFT and CASPT2 methods. No proton or hydrogen transfer is observed, but evidence is given for a hydrogen dislocation of the intramolecular hydrogen bond in the S(1) state and to lesser extent in the D(0) state. To obtain direct information on the proton/hydrogen-transfer coordinate, IR spectra are recorded both in the region of the OH and especially the CO stretching vibrations by also applying two new variants of combined IR/UV spectroscopy for the S(1) and D(0) states. The CO groups are directly involved in the hydrogen bond and, in contrast to the hydrogen-bonded OH groups, the CO stretching frequencies can be observed in all electronic states.
authors.affiliation: Fachbereich Chemie, TU Kaiserslautern and research center OPTIMAS, Erwin-Schrödinger-Str. 52, 7663 Kaiserslautern, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Fricke
authors.forename: Kristina
authors.initials: K
authors.lastname: Bartl
authors.forename: Andreas
authors.initials: A
authors.lastname: Funk
authors.forename: Andreas
authors.initials: A
authors.lastname: Gerlach
authors.forename: Markus
authors.initials: M
authors.lastname: Gerhards
mesh_terms: D005841:Gentisates / Q000737:chemistry*; D006859:Hydrogen; D011522:Protons; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013057:Spectrum Analysis
chemical_list: D005841:Gentisates; D011522:Protons; D006859:Hydrogen