INFRARED-DEPLETION SPECTROSCOPY STUDY ON HYDROGEN-BONDED FLUOROBENZENE-METHANOL CLUSTERS

Infrared-depletion spectroscopy, a double resonance method combining i nfrared-with resonant two-photon ionization (R2PI)-spectroscopy has be en applied to mixed molecular aggregates of fluorobenzene (methanol)(n ) (Fb . MeOH) with n less than or equal to 4. From the IR spectra in t he region of the OH stretching vibration-of methanol it can be shown t hat the solvent moiety forms subclusters on one side of the aromatic r ing. For Fb .(MeOH)(3) the methanol trimer exhibits a linear as well a s a cyclic structure. The different shifts of the UV bands of these tw o isomeric clusters reveal the diverse character of the hydrogen bonds involved in their formation. Furthermore it can be shown that for bot h isomeric forms the product anisole(+) is formed in equal quantities by an intracluster S(N)2 reaction following the photoionization of the chromophore. Whereas for Fb .(MeOH)(2) this reaction is in competitio n with evaporative fragmentation it is the dominant reaction channel f or the Fb .(MeOH)(3) cluster. (C) 1997 American Institute of Physics.