			10min:

CHARACTERIZATION OF WEAKLY BOUND HCF₃--OCS, H₂CF₂--OCS, H₃CF--OCS, AND HCF₃--CO₂ VAN DER WAALS COMPLEXES BY AB INITIO CALCULATIONS AND MICROWAVE SPECTROSCOPY..

MICHAL M. SERAFIN, SEAN A. PEEBLES, Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 61920 USA.

High 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 ab initio calculations at the MP2/6-311++G(2d, 2p) level have provided good agreement with the observed experimental values. The structures of HCF₃--OCS and H₂CF₂--OCS have been determined from experimentally obtained rotational spectra fit to a Watson A reduction Hamiltonian to within 4 kHz. The a -type rotational spectrum of H₃CF--OCS has been assigned, however, b -type transitions still need to be located. The HCF₃--CO₂ spectrum showed a doubling of transitions into A and E states (by up to 1.5 MHz), and is currently fit to approximately 20 kHz using XIAM. 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 Å and O=C cdots C bond angles of 61-64^\circ, although with a wider range of H--C cdots C angles ( ca. 60^\circ to 75^\circ). Results for all members of the series will be presented and compared to theoretical data.