Knowledge Bank

The intermolecular potential between aromatic and water moieties is of considerable interest because of its important role in determining properties such as immiscibility of the bulk liquids and the conformational preferences of biomolecules in aqueous solution. In order to deepen our understanding of such systems, we have carried out detailed R2PI studies on benzene-$H2O$ and benzene-$(H2O)2$ clusters formed in a supersonic expansion. Spectroscopic evidence is presented indicating in the 1:1 complex the $H2O$ molecule is on the six-fold axis in a $\pi$ hydrogen-bonding configuration with free internal rotation about this axis. Rotational band contours have been obtained of the 1:1 complexes of benzene with $H2O$, HDO, and $D2O$ at $0.08cm-1$ resolution. The class structure and character table of a new molecular symmetry group, $G24$, associated with these complexes has been constructed for the analysis. For the 1:2 complex the rotational band contour indicates the two water molecules bind to benzene on the same side of the benzene ring, with a $H2O-H2O$ separation close to that in the water dimer. The van der Waal’s structure of the 1:1 and 1:2 complexes and their isotopomers has been analyzed and tentative assignments are presented.