The Microwave Spectra of Fluorobenzene–H2O and 1,4-Difluorobenzene–H2O: Structure and Internal Rotation Analysis.
Heinrich Mäder
Institut für Physikalische Chemie, Universität Kiel, Olshausenstr. 40, D-24098 Kiel, Germany
Kai Brendel and Wolfgang Jäger
Department of Chemistry, University of Alberta, Edmonton AB T6G 2G2, Canada
Large amplitude motions often occur in weakly bound molecular dimers because the attractive forces involved are at least an order of magnitude smaller than those in chemically bound species. These motions can have noticeable effects on the rotational spectra as obtained by FTMW spectroscopy.
In the case of the 1,4-difluorobenzene–H2O dimer a small splitting of the rotational transitions can be observed which can be interpreted as the result of a hindered rotation of the water moiety about its C2 axis. The two transitions then correspond to the Σ = 0 and the Σ = 1 component of the ground internal rotor state, respectively. a similar splitting was also observed in the newly assigned microwave spectrum of the fluorobenzene–H2O dimer, suggesting that the corresponding interaction potentials share common features. In order to achieve a better understanding of the resulting intermolecular dynamics we used the flexible model developed by Meyer to analyse the experimental data. This model yields a potential function for the internal rotation and effective rotational constants for the respective internal rotor states.
The results of the analysis and a comparison with the data obtained from high level ab initio calculations will be presented.