Rotational spectra of 1-chloro-2-fluoroethylene. II. Equilibrium structures of the cis and trans isomer.

Equilibrium structures for the cis and trans isomer of 1-chloro-2-fluoroethylene are reported. The structures are obtained within a least-squares fit procedure using the available experimental ground-state rotational constants for various isotopic species of both forms. Vibrational effects were eliminated before the analysis using vibration-rotation interaction constants derived from computed quadratic and cubic force fields with the required quantum chemical calculations carried out using second-order Moller-Plesset perturbation as well as coupled-cluster (CC) theory. The semiexperimental or empirical equilibrium geometries obtained in this way agree well with the corresponding theoretical predictions obtained from CC calculations [at the CCSD(T) level] after extrapolation to the complete basis-set limit and inclusion of core-valence correlation corrections. The present results allow a detailed analysis of the geometrical differences between the two forms of 1-chloro-2-fluoroethylene. They are also compared to the structural data available for other halogenated ethylenes.