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 14N quadrupole nuclei. The observed g-tensor elements are gaa = - 0.07498(14), gbb = - 0.12531(13), and gcc = 0.06346(12) for pyrazole and gaa = - 0.09339(16), gbb = - 0.10444(14), and gcc= 0.06051(15) for imidazole. The values for the magnetic susceptibility anisotropies in units of 10-6 erg/(G2 mol) are 2Xaa - Xbb - Xcc = 39.53(24) and 2Xbb - Xcc - Xaa = 51.20(21) for pyrazole and 2xaa - Xbb - Xcc = 45.76(31) and 2Xbb - Xcc - Xaa = 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 Xcc 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.