Millimeter-wave spectrum of ClCN observed in a DC glow discharge and ab initio calculations

The ground state (v=0) millimeter-wave rotational spectrum of cyanogen chloride (ClCN) and some of its isotopic species have been investigated in the frequency region: 40.0–75.0 GHz. ClCN was produced by DC discharge through a mixture of 3-chlorobenzonitrile and tri-chloroethylene. The millimeter-wave spectrometer used is a source-modulated system combined with a free space glass discharge cell. Millimeter-wave radiation has been produced using a frequency multiplier, the fundamental radiation source being klystrons. The quadrupole hyperfine structures of 35Cl and 37Cl have been resolved, measured and analyzed. Finally, internuclear distances of ClCN have been determined using the Kraitchman's equation and compared with the previously reported values. Satisfactory agreements between the DFT-B3LYP/6-311++g(3d,3p) calculations and experimental values were found for internuclear distances and dipole moment. Based on the results of ab initio calculations at the MP4 level, ClCN was found to have a bent structure in the first excited electronic state.