Rotational spectra and structures of Rg-C₆H₆-H₂O trimers and the Ne-C₆H₆ dimer (Rg=Ne, Ar, or Kr)

Abstract

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 Å for Ne, Ar, and Kr compared to the corresponding distance in the Rg-C₆H₆ dimer. On the other hand, the c.m. (C₆H₆) to c.m. (H₂O) distance in the trimers is increased by only about 0.003 Å from its distance in the dimer. Symmetric top spectra of ²⁰Ne-C₆H₆ and ²²Ne-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 C₆ axis from the a axis in the dimers (∼19 deg) and trimers (∼21 deg) and of the displacement of the C₂ axis of the water from the a axis in the trimers (∼37 deg).