PROTON-TRANSFER REACTION IN PHENOL-(NH$3) n$ CLUSTERS: VIBRONIC SPECTRA MEASURED VIA THE $(NH_{3})_{1-1}H^{+}$ ION YIELDS
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Date
1997
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Publisher
Ohio State University
Abstract
When ionizing phenol-ammonia clusters in a supersonic jet expansion between 276 and 285 nm under 1-color 2-photon conditions, the proton transfer $(NH_{3})_{1-4}H^{+}$ ion yields depend distinctly on the excitation wavelength. The $S_{1}$-vibronic spectra measured via the phenol $(NH_{3})_{1-4}{^{+}}$ - and the $(NH_{3})_{1-4}H^{+}$ ion yields show a 1:1 correspondence with only small or none sign of phenol $(NH_{3})_{n+1} S_{1}$ - bands in the $(NH_{3})_{n}H^{+}$ -spectra (i. e., little fragmentation after proton transfer). The proton transfer yield spectra allow high quality measurements of the $S_{1}$ vibronic resonances at $n>3$, where the phenol $(NH_{3})_{n}$ spectra themselves show little structure. The data show enhanced $(NH_{3})_{1}H^{+}$ ion yield after excitation of the phenol $(NH_{3})_{1} S_{1}$ - electronic origin demonstrating proton transfer even in the n=1 cluster at sufficient phenol $(NH_{3})_{1}^{+}$ ion excess energy ($\geq 8000 cm^{-1}$ at 2-photon absorption). Underlying the sharp phenol $(NH_{3})_{n} S_{1}$ - bands we observe broad spectral features which extend to the red of the phenol $(NH_{3})_{n}$ spectra and resemble somewhat to the electronic spectrum of the phenolatanion $PhO^{*}$. We very tentatively assign the spectrum to excitation to the $PhO^{*} H^{+} (NH_{3})_{n}$ charge transfer state. Structure and dynamics of phenol $(NH_{3})_{2}$ and phenol-$d_{1}-(ND_{3})_{2}$ are discussed in detail based on the observed $S_{1}$ intermolecular vibrations and tunnel splittings in comparison to results from ab initio calculations.
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Author Institution: Institut f\""ur Physikalische Chemie und Elektrochemie, Universit\""at D\""usseldorf