Dirac-Fock calculations of magnetic shielding constants: hydrogen moleculeand hydrogen halides

Proton magnetic shielding constants of HX (X = H, F, Cl, Br, I) are calcula ted based on the Dirac-Fock finite perturbation (DF-FP) method. The results are in good agreement with experiments: the halogen dependence of the prot on chemical shifts is well reproduced. The Gordon decomposition for the mag netic shielding constant gives results closely parallel to the lowest-order (c(-2)) terms in the traditional quasi-relativistic theories; the so-calle d diamagnetic, paramagnetic, spin-dipolar, and Fermi-contact terms. This de composition shows that the Fermi-contact term is the most important origin of the relativistic effect on the chemical shift, as is well known in the q uasi-relativistic theories. (C) 1999 Elsevier Science B.V. All rights reser ved.