CHARACTERIZATION OF WEAKLY BOUND HCF$_3$--OCS, H$_2$CF$_2$--OCS, H$_3$CF--OCS, AND HCF$_3$--CO$_2$ VAN DER WAALS COMPLEXES BY AB INITIO CALCULATIONS AND MICROWAVE SPECTROSCOPY

Author Institution: Department of Chemistry, Eastern Illinois University, 600; Lincoln Ave., Charleston, IL 61920 USAHigh resolution Fourier-transform microwave spectroscopy has been utilized in a systematic study of the structural and dynamic properties of a series of fluorinated methane molecules complexed to carbonyl sulfide and carbon dioxide. Theoretical data from \textit{ab initio} calculations at the MP2/6-311++G(2d, 2p) level have provided good agreement with the observed experimental values. The structures of HCF$_3$--OCS and H$_2$CF$_2$--OCS have been determined from experimentally obtained rotational spectra fit to a Watson \textit{A} reduction Hamiltonian to within 4 kHz. The \textit{a}-type rotational spectrum of H$_3$CF--OCS has been assigned, however, \textit{b}-type transitions still need to be located. The HCF$_3$--CO$_2$ spectrum showed a doubling of transitions into \textit{A} and \textit{E} states (by up to 1.5 MHz), and is currently fit to approximately 20 kHz using XIAM} \underline{\textbf{51a}},\ (1996), 923.}. The ab initio structures of all the complexes within the series are very similar with O$\cdots$H distances consistently between 2.57-2.65 \AA\ and O=C$\cdots$C bond angles of 61-64$^{irc}$, although with a wider range of H--C$\cdots$C angles (\textit{ca.} 60$^{irc}$ to 75$^{irc}$). Results for all members of the series will be presented and compared to theoretical data