ANALYSIS OF MICROWAVE SPECTRUM, INTERNAL ROTATION AND C--H$ \cdots $F INTERACTIONS OF THE CHF$_3 \cdots $C$_2$H$_3$F WEAKLY BOUND COMPLEX

Author Institution: Department of Chemistry, Eastern Illinois University, 600 Lincoln; Ave., Charleston, IL 61920C--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 $F interactions between the TFM and VF. This near prolate asymmetric top exhibited three-fold internal rotation of the CF$_3$ 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, nderline{\textbf {51a}}, (1996), 923-932.} 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