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 χd is obtained directly by first-order perturbation theory and the paramagnetic contribution χp 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 〈χd〉Av=—9.58×10—6 erg gauss—2 mole—1 (exp: —9.2×10—6 erg gauss—2 mole—1) and 〈χp〉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.