Magnetic Properties of Water Molecule

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Abstract
The mass susceptibility χ and protonmagnetic shielding factor σ for H2O molecule are calculated using a localized electron pair LCAO MO wave function. The paramagnetic part of the susceptibility and a portion of the paramagnetic part of σ are calculated by a variational method used earlier for the H2 molecule. The relation of the present variational method to the methods employed by McGarvey and by Stephen is discussed in some detail. The calculated value of χ is found to be —0.687×10—6 in very good agreement with the experimental value of —0.699×10—6. (In an earlier report [Bull. Am. Phys. Soc. Ser. II, 3, 372 (1958)] we stated the calculated value of χ erroneously as —0.692×10—6.) The calculated value of σ is, however, found to be only —0.85×10—5 in rather poor agreement with the experimental value of —2.97×10—5. The causes for this poor agreement are analyzed, and it is concluded that the main reasons are (1) use of a rather large ionic character (66%) for the OH bond obtained from a curve of electronegativity difference versus ionic character and (2) use of undistorted H‐atom orbitals in the LCAO MO function. It is suggested that the calculated value of σ would improve in the right direction if the effective charge for the H‐atom orbital were taken as greater than unity. The value of σ is recalculated with Ellison and Shull's ``approximate treatment'' wave function and found to be —1.31×10—5. The disagreement with experiment in this case is ascribed to cause (2). Arguments are presented to show that more accurate values of σ for protons in a molecule can be obtained if in the Hamiltonian for the electrons the origin for the first‐order perturbation term due to the magnetic field is taken at the centroid of the electronic charge rather than at any other point.

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