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).