An investigation of the change of the nuclear magnetic shielding in HF on forming the Ar•••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 computation and by a classical model. The long-range classical model, which includes 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, the change in the isotropic proton shielding delta<(sigma)over bar> is -0.3 ppm and in the anisotropy delta(Delta sigma) = delta(sigma(parallel to) - sigma(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.