The Rotational Zeeman Effect of Pyrazole and Imidazole

Abstract

The rotational Zeeman effect of the most abundant isotopic species of pyrazole and of imidazole has been studied under Δ M= 0 and Δ M = ± 1 selection rules. With field close to 1.9 Tesla, the nuclear Zeeman effect uncouples the rotational angular momentum and the spins of the two nonequivalent 14 N quadrupole nuclei. The observed g-tensor elements are g aa = - 0.07498(14), g bb = - 0.12531(13), and g cc = 0.06346(12) for pyrazole and g aa = - 0.09339(16), g bb = - 0.10444(14), and g cc = 0.06051(15) for imidazole. The values for the magnetic susceptibility anisotropies in units of 10 -6 erg/(G 2 mol) are 2X aa - X bb - X cc = 39.53(24) and 2X bb - X cc - X aa = 51.20(21) for pyrazole and 2x aa - X bb - X cc = 45.76(31) and 2X bb - X cc - X aa = 42.19(41) for imidazole. (Given uncertainties are single standard deviations of the fit.) The so-called nonlocal (π-ring current) contributions to the out of plane components of the susceptibility tensor X cc nonlocal , derived as differences between the observed susceptibilities and values calculated from additivity rules for local atom susceptibilities, are compared to those derived earlier for other aromatic five membered ring molecules.