Microwave spectrum, quadrupole coupling constants, structure and ab initio calculations of N-bromocyanofluoromethanimine

Abstract

The microwave spectrum of N-bromocyanofluoromethanimine CF(CN)NBr in the ground vibrational state in the region from 18.0 to 38.0 GHz has been investigated. The assigned spectrum is only consistent with a planar molecule with the cyano group trans to the bromine atom. The hyperfine structure due to the nuclear quadrupole coupling of the bromine nucleus has been analyzed for the a-type R transitions of both the 81Br and 79Br isotopic species. Quadrupole splittings due to the 14N nuclei were not resolved. The rotational constants, the centrifugal distortion constant ΔJ, and the nonzero values of the diagonal and off-diagonal elements of the bromine quadrupole coupling tensor were determined by a least-squares fit for both isotopic species of bromine. The r0 structural parameters r(C–C), r(C–F), and ∢(N=C–C) were determined to have values of 1.422(9) and 1.349(15) Å, and 121.6(9)°, respectively, whereas other structural parameters were fixed at the values obtained for the corresponding parameters of similar molecules. The equilibrium geometry of the two possible isomeric forms of CF(CN)NBr were determined by an ab initio calculation which employed the various basis sets with and without electron correlations. These results are compared with the corresponding values of some similar molecules.