The microwave spectrum of 2-methylthiazole: methyl internal rotation and 14N nuclear quadrupole coupling

Abstract

The microwave spectrum of 2-methylthiazole has been investigated in the frequency range from 7 to 13 GHz. Rotational spectra in the two lowest states of internal methyl rotation ( m=0,±1) were measured using a pulsed molecular beam Fourier transform microwave spectrometer. The analysis of the spectra was based on a rigid frame–rigid symmetric top Hamiltonian with inclusion of first order energy contributions from 14N-nuclear quadrupole coupling, yielding the rotational constants A=5343.883(74) MHz, B=3265.914(54) MHz, C=2052.252(51) MHz, the threefold barrier to internal rotation V 3=34.938(20) cm −1, the moment of inertia of the methyl group I α=3.1651(20) u A ̊ 2, the angle between internal rotor axis i and inertial a-axis ∠( i, a)=4.462(1)°, and the nitrogen quadrupole coupling constants χ +=χ bb+χ cc=−0.5239(15) MHz, χ −=χ bb−χ cc=−5.3030(25) MHz and |χ ab|=2.2791(137) MHz. The results from this investigation are compared with results from previous microwave studies on 4- and 5-methylthiazole and 2-, 4- and 5-methyloxazole.