Infrared-depletion spectroscopy study on hydrogen-bonded fluorobenzene–methanol clusters

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Abstract
Infrared-depletion spectroscopy, a double resonance method combining infrared- with resonant two-photon ionization (R2PI)-spectroscopy has been applied to mixed molecular aggregates of fluorobenzene⋅(methanol)n (Fb⋅MeOH) with n⩽4. From the IR spectra in the region of the OH stretching vibration of methanol it can be shown that the solvent moiety forms subclusters on one side of the aromatic ring. For Fb⋅(MeOH)3 the methanol trimer exhibits a linear as well as a cyclic structure. The different shifts of the UV bands of these two isomeric clusters reveal the diverse character of the hydrogen bonds involved in their formation. Furthermore it can be shown that for both isomeric forms the product anisole+ is formed in equal quantities by an intracluster SN2 reaction following the photoionization of the chromophore. Whereas for Fb⋅(MeOH)2 this reaction is in competition with evaporative fragmentation it is the dominant reaction channel for the Fb⋅(MeOH)3 cluster.