Rotational Spectrum of the Mixed van der Waals Triad Pyridine–Ar–Ne

We report the Fourier transform microwave spectra of four isotopologues of the hetero triad pyridine–Ar–Ne, formed by the combination of two isotopes of the nitrogen atom ( 14 N and 15 N) in pyridine with two isotopes of the rare gas (RG) atoms ( 20 Ne and 22 Ne), by using pulsed jet spectroscopy. We detected the conformer denoted [1,1], with the Ne and Ar atoms located one on each side of the ring plane. The [2,0] species, with the two RG atoms on the same side of the ring, was not observed. Ab initio MP2/6‐311++G** calculations suggest the rotational spectrum of this species to be complicated by the presence of several almost equivalent minima, separated by very low barriers. Four structural van der Waals parameters, R Ar , R Ne , θ Ar and θ Ne , which localize the RG atoms with respect to pyridine, are determined. The 14 N nuclear quadrupole coupling constants are obtained for the isotopologues containing this nucleus.