Assignment and analysis of the rotational spectrum of 3-chlorobenzonitrile

The rotational spectrum of 3-chlorobenzonitrile has been assigned and measured over the frequency region 9-290 GHz, both in the static sample and in supersonic expansion. Extensive measurements are reported for the ground states of the ³⁵Cl and the ³⁷Cl isotopomers. Precise spectroscopic constants have been determined from global fits to all available data, including resolved hyperfine splitting structure due to the presence of the chlorine and the nitrogen quadrupolar nuclei. Principal nuclear quadrupole tensors are derived for both ³⁵Cl and ¹⁴N nuclei in the parent isotopomer, and the results are compared with those for related molecules. The values of all spectroscopic constants are confronted with predictions from ab initio calculations in order to assess the utility of the array of simple techniques employed to increase quantitative accuracy of such predictions.