A revised experimental absolute magnetic shielding scale for oxygen

A revised absolute magnetic shielding scale for oxygen is established based on a recently reported highly precise experimental measurement of the O17 spin-rotation constant in carbon monoxide. The isotropic oxygen magnetic shielding constant for C12O17 at the equilibrium geometry, σe, is found to be −56.8±0.6 ppm. The experimental rovibrationally averaged value of the shielding constant at 300 K, 〈σ〉300 K, is −62.7±0.6 ppm, in excellent agreement with the ab initio value reported by Vaara et al. [J. Chem. Phys. 109, 8388 (1998)]. Based on the revised scale and on experimentally known oxygen chemical shifts, 〈σ〉300 K (H2O(l)) is 287.5±0.6 ppm and 〈σ〉300 K (H2O(g)) is 323.6±0.6 ppm.