HELEN O. LEUNG, MARK D. MARSHALL, Department of Chemistry, Amherst College, P.O. Box 5000, Amherst, MA 01002-5000.
Guided by previous studies of the 35Cl and 37Cl isotopomers of 1-chloro-1-fluoroethylene,\footnoteR.~G.~Stone and W.~H.~Flygare, J.~Mol.~Spectrosc. \textbf\underline32, 233 (1969); J.~L.~Alonso, A.~G.~Lesarri, L.~A.~Leal, and J.~C.~López, J.~Mol.~Spectrosc. \textbf\underline162, 4 (1993). we have collected the spectra of these and four additional naturally occurring isotopomers in the 7--21 GHz region with a Fourier transform microwave spectrometer. The rotational transitions are split by both the chlorine nuclear quadrupole and the nuclear spin-rotation hyperfine interactions. The rotational constants, together with the hyperfine coupling constants and guidance from ab initio calculations, allow a precise determination of the structure of the 1-chloro-1-fluoroethylene monomer, which in turn aids our work on structure determination for complexes involving this molecule. For the acetylene--1-chloro-1-fluoroethylene complex, we have collected the rotational spectra for five of its isotopomers. The transitions are once again split by chlorine nuclear quadrupole coupling. The spectroscopic constants are consistent with a planar structure in which a hydrogen bond is formed between an H atom in HCCH and the F atom in 1-chloro-1-fluoroethylene with a second interaction between the H atom located cis to the hydrogen-bonded F atom in 1-chloro-1-fluoroethylene and the acetylenic bond.