Millimeter-Wave Rotational Spectrum, Barrier to Internal Rotation, and DFT Calculation of o-Tolunitrile

The millimeter-wave rotational spectra of o-tolunitrile (C6H4CH3CN) have been investigated in the ground torsional state in the frequency range 50.0–75.0 GHz. Many high-J rotational lines with large A-E splitting due to internal rotation of the methyl top have been assigned. A least squares analysis of the A-E splitting of 92 transitions resulted in the determination of accurate values of internal rotation parameters. The observed parameters were compared with the previously reported experimental values and DFT calculation results.