Molecular structure of cis-1-chloro-2-fluoroethylene from ab initio calculations and microwave spectroscopy

The molecular structure of cis-1-chloro-2-fluoroethylene has been investiga ted both theoretically and experimentally. As far as ab initio computations are concerned, the equilibrium geometry has been evaluated using the coupl ed-cluster approach [CCSD(T)] and basis sets of triple and quadruple zeta q uality. Accurate results are presented. A recommended equilibrium geometry, obtained by adding ad hoc corrections, is also given. The centimetre and m illimetre-wave spectra of the following 8 isotopomers have been observed: ( CDCl)-Cl-35=CHF, (CDCl)-Cl-37=CHF, (CHCl)-Cl-35=CDF, (CHCl)-Cl-37=CDF, (CDC l)-Cl-35-CDF, (CDCl)-Cl-37-CDF, (CHCl)-C-13-Cl-35-CHF, (CHCl)-Cl-35=(CHF)-C -13. Ground state rotational and quartic centrifugal distortion constants a nd diagonal elements of the nuclear quadrupole tensor (for both Cl-35 and C l-37) have been accurately determined. The structure of cis-1-chloro-2-fluo roethylene has been experimentally determined for the first time by isotopi c substitution, employing three independent methods. A comparison between t he experimental and theoretical geometry is also presented.