THE STRUCTURE AND PHOTOPHYSICS OF CLUSTERS OF IMMISCIBLE LIQUIDS - C6H6-(H2O)N

Mixed clusters of C6H6 and H2O of type C6H6-(H2O)n where n = 1-5 have been studied using one-color resonance-enhanced two-photon ionization coupled with time-of-flight mass spectrometric detection. The 1:1 complex is seen to have an electronically forbidden origin with intensity at least 1000 times less than that at 6(0)1. The H2O molecule thus lies on the sixfold axis of benzene and is undergoing free internal rotation about this axis. The blue-shift and high efficiency of fragmentation of the 1:1 complex argue for hydrogen bonding of the H2O molecule to the benzene pi-cloud. The 1:2 complex induces a strong origin with intensity 14% of that at 6(0)1. The rotational band contour yields a geometry in which the two water molecules bind to benzene on one side of the benzene ring, with a H2O-H2O separation close to that in the water dimer. Higher 1:n clusters show spectra which suggest structures involving a network of hydrogen bonded water molecules building up away from the benzene ring, consistent with a microscopic immiscibility of C6H6 and H2O.