INVESTIGADORES
GOMEZ sergio Santiago
artículos
Título:
Relativistic Heavy atom effect in Heavy atom (HAHA) shieldings in group-14 and 15 hydrides
Autor/es:
PERTTU LANTTO; JUHA VARA; RODOLFO ROMERO; SERGIO GOMEZ; AND GUSTAVO AUCAR
Revista:
JOURNAL OF CHEMICAL PHYSICS
Editorial:
AMER INST PHYSICS
Referencias:
Año: 2006 vol. 125 p. 1841131 - 18411313
ISSN:
0021-9606
Resumen:
The principal relativistic heavy-atom effects on the nuclear magnetic resonance (NMR) shielding tensor of the heavy atom itself (HAHA effects) are calculated using ab initio methods at the level of the Breit-Pauli Hamiltonian. This is the first systematic study of the main HAHA effects on nuclear shielding and chemical shift by perturbational relativistic approach. The dependence of the HAHA effects on the chemical environment of the heavy atom is investigated for the closed-shell X2+, X4+, XH2, and XH3(X=Si–Pb) as well as X3+, XH3, and XF3 (X=P–Bi) systems. Fully relativistic Dirac-Hartree-Fock calculations are carried out for comparison. It is necessary in the Breit-Pauli approach to include the second-order magnetic-field-dependent spin-orbit (SO) shielding contribution as it is the larger SO term in XH3-, XH3, and XF3, and is equally large in XH2 as the conventional, third-order field-independent spin-orbit contribution. Considering the chemical shift, the third-order SO mechanism contributes two-thirds of the difference of 1500 ppm between BiH3 and BiF3. The second-order SO mechanism and the numerically largest relativistic effect, namely the Mass Correction term, are isotropic and practically independent of electron correlation effects as well as the chemical environment of the heavy atom. The third-order SO terms depend on these factors and contribute both to heavy-atom shielding anisotropy and NMR chemical shifts. Although the non relativistic theory gives correct chemical shift trends in present systems, the third-order SO-I terms are necessary for more reliable predictions.