15min:

JOCHEN KÜPPER, KLAAS NAUTA AND ROGER E. MILLER, University of North Carolina, Department of Chemistry, Chapel Hill, NC 27599.

Infrared spectra are reported for several (C₆H₆)_m-(HCN)_n and (C₆D₆)_m-(HCN)_n clusters in liquid helium nanodroplets. A large electric field can be used to collapse the rotational structure in these spectra, which aids in the initial searching. In the 1:1 clusters the HCN _\mathrmCH stretching vibration at 3253.2~cm\textsuperscript-1 (C₆H₆-HCN) and 3252.9~cm^-1 (C₆D₆-HCN) are red-shifted by approximately 60~cm\textsuperscript-1 compared to the monomer, indicative of strong intermolecular hydrogen bonds between the CH-group and the aromatic -clouds of the benzenes. Zero field spectra show considerable rotational structure consistent with a symmetric rotor structure as determined in the gas-phase by microwave spectroscopy.

Moreover several trimers and tetramers of HCN and Benzene have been observed, all of which are further red-shifted than the 1:1 complexes. Pressure-dependency studies allow the size assignments of these clusters. The frequency shifts and rotational contours of the bands allows one to infer the structures of these clusters in liquid helium.