Spin Rotation Constant and Rotational Magnetic Moment of 13C16O

13C16O has been studied by the molecular-beam magnetic-resonance method in the high-field limit. Two different spectra were observed. These correspond, first, to the reorientation of the carbon-13 nuclear spin with respect to the external field H, and second, to the reorientation of the rotational angular momentum with respect to H. By analyzing these spectra with third-order perturbation theory, it was found that the carbon-13 spin–rotation constant c = − (32.59 ± 0.15) kHz, and that the rotational gyromagnetic ratio gJ = −(0.25691 ± 0.00020) nm. From this measurement of gJ and the known value of the molecular quadrupole moment, the anisotropy constant f of the susceptibility tensor has been determined. It was shown that f / H2 = + (38.9 ± 3.9) × 10−5Hz G−2. By combining the present results for c and gJ with Huo's ab initio calculations of the ground-state electronic properties of the molecule, the average carbon-13 shielding constant σa and the mean diamagnetic susceptibility ξa have been evaluated. These are: σa = 5.0 × 10−6 and ξa = − 203 × 10−31erg G−2·molecule−1. A simple method of determining the sign of c in terms of the sign of gJ by inserting an obstacle into the molecular beam is described.