High-resolution ultraviolet spectroscopy of p-fluorostyrene-water: evidence for a σ-type hydrogen-bonded dimer

Abstract

Ab initio calculations predict four stable conformational structures of the singly hydrated cluster of p-fluorostyrene: two out of plane with π- and two in plane with σ-type intermolecular hydrogen bonding between p-fluorostyrene and water. We employed mass-selective resonance-enhanced two-photon ionization high-resolution (70-MHz FWHM laser bandwidth) spectroscopy to partially resolve the rotational structure of the 0⁰₀ origin band of the S₁←S₀ electronic transition. A computer-aided fit based on genetic algorithms was used to analyze the experimental high-resolution spectrum and to determine the observed conformational structure. The good agreement between the experimental and the simulated spectra of the 0⁰₀ band and the assignment of the other prominent bands as inter- and intramolecular vibrational progressions clearly demonstrates that the anti in-plane conformer is the most abundant one in the molecular beam. The existence of the σ-type hydrogen bond between p-fluorostyrene and water manifests that the electron attracting effect of fluorine dominates over the releasing mesomeric effect of the vinyl group and thus a π-type hydrogen bonding with the aromatic ring is not favored in this case.