ROTATIONAL SPECTRA AND STRUCTURES OF RG-C6H6-H2O TRIMERS AND THE NE-C6H6 DIMER (RG=NE, AR, OR KR)

Rotational spectra of Rg-C6H6-H2O isotopomers, where Rg=Ne, Ar, or Kr, have been observed with a Balle-Flygare Fourier transform microwave spectrometer. In these trimers the benzene is sandwiched between the rare gas and H2O. Isotopic substitution and inertial analyses show that the Rg-C6H6 distance in the trimer is reduced by about 0.01 Angstrom for Ne, Ar, and Kr compared to the corresponding distance in the Rg-C6H5 dimer. On the other hand, the c.m. (C6H6) to c.m. (H2O) distance in the trimers is increased by only about 0.003 Angstrom from its distance in the dimer. Symmetric top spectra of Ne-20-C6H6 and Ne-22-C6H6 were observed as an aid in the comparison. Hyperfine structure (hfs) and substitution analyses with HDO/D2O containing isotopomers reveal that the m = 0 and 1 states of H2O in the trimer are virtually unchanged from those in the C6H6-H2O dimer, including essentially free rotation. In addition, analyses are made of the root-mean square (rms). deviation for the benzene C-6 axis from the a axis in the dimers (similar to 19 deg) and trimers (similar to 21 deg) and of the displacement of the C-2 axis of the water from the a axis in the trimers (similar to 37 deg).