Molecular g Values, Magnetic Susceptibility Anisotropies, Second Moments of the Electronic Charge Distribution, and Molecular Quadrupole Moments in Pyridine

Abstract

The high-field linear and quadratic Zeeman effect has been observed in pyridine. The spectra is complicated by the presence of the 14N nuclear quadrupole coupling. Perturbation theory through second order is used to extract the molecular Zeeman parameters. The molecular g values are gaa = − (0.0770 ± 0.0005), gbb = − (0.1010 ± 0.0008), and gcc = 0.0428 ± 0.0004. The magnetic susceptibility anisotropies are (2χaa − χbb − χcc) = (54.3 ± 0.6) × 10−6 and (2χbb − χaa − χcc) = (60.5 ± 0.8) × 10−6 in units of erg/gauss2·mole. The a axis bisects the CNC angle and the b axis is also in the molecular plane. The molecular quadrupole moments are Qaa = − (3.5 ± 0.9), Qbb = 9.7 ± 1.1, Qcc = − (6.2 ± 1.5) all in units of 10−26 esu·cm2. Using the known molecular structure and the molecular g values gives the diagonal elements in the paramagnetic susceptibility tensor and the anisotropies in the second moment of the electronic charge distribution. These results are χaap = 241.5 ± 1.5, χbbp = 247.4 ± 2.0, and χccp = 393.9 ± 2.0 all in units of 10−6 erg/G2·mole and 〈a2〉 − 〈b2〉 = 0.92 ± 0.80, 〈b2〉 − 〈c2〉 = 48.28 ± 0.60, and 〈c2〉 − 〈a2〉 = − 49.19 ± 0.60 all in units of 10−16 cm2. Combining the above values with the known bulk magnetic susceptibility gives the individual diagonal elements in the total and diamagnetic susceptibility ternsors. The individual values of 〈a2〉, 〈b2〉, and 〈c2〉 are also obtained. The results are compared to other ring compounds.