			10min:

ANALYSIS OF MICROWAVE SPECTRUM, INTERNAL ROTATION AND C--H cdots

F INTERACTIONS OF THE CHF₃ cdots

C₂H₃F WEAKLY BOUND COMPLEX.

LENA F. ELMUTI, DANIEL A. OBENCHAIN, REBECCA A. PEEBLES, SEAN A. PEEBLES, Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 61920.

C--H cdots X hydrogen bonds with systematic variation of halogens (X = F, Cl, Br) have been examined using Fourier-Transform Microwave (FTMW) spectroscopy. Rotational constants for trifluoromethane--vinyl fluoride (TFM cdots VF) were consistent with a C_{\textrm s} symmetry structure that exhibited both bifurcated and single C--H cdots F interactions between the TFM and VF. This near prolate asymmetric top exhibited three-fold internal rotation of the CF₃ group causing characteristic doubling in its spectra.

Initial assignments were completed using chirped-pulse FTMW spectroscopy with additional measurements made using a resonant-cavity FTMW spectrometer. Rotational constants from ab initio calculations at the MP2/6-311++G(2d,2p) level were in agreement with preliminary experimental values (A= 4828 MHz, B = 1049 MHz, C= 1018 MHz). XIAM was used to provide the barrier to internal rotation (25(5) cm^-1) and other spectral information. Spectroscopic parameters for the normal isotopic species as well as preliminary structural results on the C--H cdots F interactions in this complex will be presented.