Toward an absolute NMR shielding scale using the spin-rotation tensor within a relativistic framework

AUCAR, GUSTAVO ADOLFO; GOMEZ, SERGIO SANTIAGO; GIRIBET, CLAUDIA GLORIA; AUCAR, IGNACIO AGUSTÍN

North Dakota

Conferencia; IX International Society for Theoretical Chemical Physics (ISTCP) Conference; 2016

International Society for Theoretical Chemical Physics

One of the most influencing articles showing the best way to get absolute values of the NMR magnetic shielding, $sigma$ (which is non measurable) from both, accurate measurements and theoretical calculations, was published long time ago by Flygarecite{Flygare74}. His model was shown to break down when heavy atoms are involved.This fact motivated the development of new theories of nuclear spin-rotation (SR) tensors, that consider electronic relativistic effectscite{aucar2012}; and also fewproposals to extend Flygare´s model.In this poster we show new different models that generalize that of Flygare. All of them are written using four-component relativistic expressions, though the two-component relativistic SO-S term also appears in one. The first clues for these developments were taken from the relationship among $sigma$ and the SR tensors within the two-component relativistic LRESC modelcite{LRESC}. Besides, we introduced few other well defined assumptions:i) relativistic corrections must be included in a way to best reproduce the relationship among the (e-e) term (called ?paramagnetic? within the non-relativistic domain) of $sigma$ with its equivalent part of the SR tensor,ii) as happens in Flygare´s rule, the shielding of free atoms shall be included to improve accuracy. In the highest accurate of our models, a new term that arise as spin-orbit effect due to spin, SO-S (a mechanism in which the spin-Zeeman Hamiltonian replace the orbital-Zeeman Hamiltonian) is included.The best of our models, has a resemblance to that of Flygare. We shall show results of the application of those models to halogen containing linear molecules.