A molecular beam Fourier transform microwave study of0-tolunitrile:14N nuclear quadrupole coupling and methyl internal rotation effects

The high resolution microwave spectrum of o-tolunitrile (o-CH3C6H4CN) has been investigated in the torsional ground state in the frequency range 8–18 GHz by molecular beam Fourier transform microwave spectroscopy. Results include a 14N quadrupole hyperfine interaction, a fourth-order centrifugal distortion, and a methyl internal rotation analysis. Effects of centrifugal distortion on the internal rotation were included, yielding a standard deviation of the fit of the order of the experimental uncertainty. The structural rotational constants were determined to be A = 2891.6469(5) MHz, B = 1499.8809(1) MHz, and C = 993.521 70(6) MHz. Furthermore, analysis of the hyperfine structure of the rotational lines yielded the nitrogen quadrupole coupling constants χ aa = -4.094(2) MHz and χ bb −χ cc = 0.191(6) MHz. The threefold barrier for internal rotation of the methyl group was V 3 = 187.699(3) cm−1 and the angle between the internal rotor axis and the principal a axis was θ = 53.591(2)°. The internal rotation parameters are in good agreement with published results of Jaman et al. [1998, J. molec. Spectrosc., 192, 148].