An investigation of the change of the nuclear magnetic shielding in HF on forming the Ar center dot center dot center dot HF complex

The effect of the argon atom on the magnetic shielding tensor at the proton and fluorine nuclei in Ar...HF has been studied by SCF/GIAO ab initio comp utation and by a classical model. The long-range classical model, which inc ludes the electric and magnetic terms, gives good agreement for the change of the H shielding anisotropy. The magnetic term dominates the H shielding change; the electric field and field gradient contributions to the electric term are of opposite sign. At the experimental intermolecular distance, th e change in the isotropic proton shielding delta<(sigma)over bar> is -0.3 p pm and in the anisotropy delta(Delta sigma) = delta(sigma(parallel to) - si gma(perpendicular to)) it is 6.6 ppm. This large increase in the anisotropy arises from the magnetizability of the Ar atom and the linearity of the F- H...Ar bond.