Magnetic Properties of Hydrogen Fluoride. II. Susceptibility

Abstract

A method is outlined for the calculation of the magnetic susceptibility χ from the ground‐state wave function of ¹Σ molecules. The diamagnetic contribution χ^d is obtained directly by first‐order perturbation theory and the paramagnetic contribution χ^p is determined by a variational technique based on minimizing the second‐order energy in an external magnetic field. When applied to an SCF—LCAO—MO function for hydrogen fluoride, the theoretical result is 〈χ〉_Av=—8.74×10^—6 erg gauss^—2 mole^—1, in excellent agreement with the experimental value of —8.6×10^—6 erg gauss^—2 mole^—1. The separate contributions, with respect to the fluorine as origin, are somewhat more in error, with 〈χ^d〉_Av=—9.58×10^—6 erg gauss^—2 mole^—1 (exp: —9.2×10^—6 erg gauss^—2 mole^—1) and 〈χ^p〉_Av=0.855×10⁶ erg gauss^—2 mole^—1 (exp: 0.609×10^—6 erg gauss^—2 mole^—1, as obtained from the rotational magnetic moment). For the isoelectronic atoms F^— and Ne (in which there is only a diamagnetic term), analytic Hartree‐Fock functions yield 〈χ〉_Av values equal to —12.7×10^—6 erg gauss^—2 mole^—1 (exp: ∼—12×10^—6) and —7.48×10^—6 erg gauss^—2 mole^—1 (exp: —6.7 to —7.7×10^—6), respectively. By a comparison of the results obtained with different molecular wave functions for hydrogen fluoride (one‐center and two‐center approximations), the sensitivity of the magnetic‐susceptibility components (especially the paramagnetic terms) to the form of the wave function is clearly demonstrated. This suggests that χ and its components can serve as useful criteria for the accuracy of electron distributions and indicates the need for refinements in the hydrogen fluoride functions. Finally, the availability of a method for the theoretical evaluation of the susceptibility tensor components suggests that additional measurements should be done to improve the experimental values.