Knowledge Bank

Guided by previous studies of the $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$Cl and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$Cl isotopomers of 1-chloro-1-fluoroethylene,},} 233 (1969); J. L. Alonso, A. G. Lesarri, L. A. Leal, and J. C. Lopez, J. Mol. Spectrosc. \textbf{\underline{162},} 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 \textit{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 \textit{cis} to the hydrogen-bonded F atom in 1-chloro-1-fluoroethylene and the acetylenic bond.