Investigation of the quadrupole coupling hyperfine structure due to two nuclei by molecular beam Fourier transform microwave spectroscopy: spectra of dichlorofluoromethane and pyridazine

Abstract

The nuclear quadrupole coupling hyperfine structure arising in the rotational spectra of dichlorofluoromethane and pyridazine due to the presence of two equivalent quadrupolar nuclei (Cl and N, respectively) has been investigated using molecular beam Fourier transform microwave spectroscopy in the 6–18 GHz frequency range. For dichlorofluoromethane the species CH 35Cl 2F, CH 35Cl 37ClF and CH 37Cl 2F have been investigated whereas for pyridazine only the parent species with two 14N has been observed. Thanks to the sub-Doppler resolution and high sensitivity inherent to this technique, the hyperfine structure for the low J transitions has been resolved and the complete nuclear quadrupole coupling tensors have been determined. Diagonalization of the tensor for dichlorofluoromethane molecule has given interesting information which reveals very small deviations between the Cl nuclei quadrupole coupling tensors principal axes z and the ClC bonds. The experimental results have been compared with those from MP4/6-311+G(2d,2p) ab initio calculations.