Inversion, internal rotation, and nitrogen nuclear quadrupole coupling of p-toluidine as obtained from microwave spectroscopy and ab initio calculations

Abstract

A highly accurate combined experimental and theoretical investigation has been conducted on p-toluidine (4-methylaniline) in its vibrational and electronic ground state. Rotational transitions have been recorded using pulsed molecular beam Fourier transform microwave (MB-FTMW) spectroscopy in the frequency range 7–20 GHz. The rotational spectrum of this molecule is complicated by the inversion of the amino group, the internal rotation of the methyl group, and the 14N nuclear quadrupole hyperfine structure. Second-order Møller–Plesset perturbation theory and coupled-cluster singles-and-doubles with a perturbative correction for connected triples have been used in conjunction with high-level basis sets for the quantum chemical investigation. The torsional fine and quadrupole hyperfine structures of the spectra could be interpreted by means of these theoretical data.