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

GUSTAVO A. AUCAR; IGNACIO AGUSTIN AUCAR; SERGIO GÓMEZ; CLAUDIA G. GIRIBET

Grand Forks

Congreso; International Society of Theoretical and Computational Physical Chemistry; 2016

ISTCP

One of the most influencing articles showing the best way to get absolute values of the NMR magnetic shielding, σ (which is non measurable) from both, accurate measurements and theoretical calculations, was published long time ago by Flygare. 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 effects [1]; and also few proposals to extend Flygares model [2].In this poster presentation we will 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 σ and the SR tensors within the two-component relativistic LRESC model [3]. 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 σ with its equivalent part of the SR tensor, ii) as happens in Flygares 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.[1] I. A. Aucar, S. S. Gomez, M. C. Ruiz de Azúa and C. G. Giribet, J. Chem. Phys., 136, 204119 (2012); Y. Xiao and W. Liu, J. Chem. Phys., 138, 134104 (2013).[2] E. Malkin et al, J. Phys. Chem. Lett., 4, 459 (2013); Y. Xiao et al, J. Chem. Theory Comput., 10, 600 (2014); T. B. Demissie et al, J. Chem. Phys., 143, 164311 (2015); T. B. Demissie, Phys. Chem. Chem. Phys., 18, 3112 (2015).[3] J. I. Melo et al, J. Chem. Phys., 118, 471 (2003).