Relativistic and QED effects on NMR magnetic shielding constant of neutral and ionized atoms and diatomic molecules

Relativistic and quantum electrodynamics effects on NMR shielding tensors of TlX (X = H, F, Cl, Br, I, At) molecules

The results of relativistic calculations of nuclear magnetic resonance shielding tensors (σ) for the thallium monocation (Tl+), thallium hydride (TlH), and thallium halides (TlF, TlCl, TlBr, TlI, and TlAt) are presented as obtained within a four-component polarization propagator formalism and a two-component linear response approach within the zeroth-order regular approximation. In addition to a detailed analysis of relativistic effects performed in this work, some quantum electrodynamical (QED) effects on those nuclear magnetic resonance shieldings and other small contributions are estimated. A strong dependence of σ(Tl) on the bonding partner is found, together with a very weak dependence of QED effects with them. In order to explain the trends observed, the excitation patterns associated with relativistic ee (or paramagnetic-like) and pp (or diamagnetic-like) contributions to σ are analyzed. For this purpose, the electronic spin-free and spin-dependent contributions are separated within the two-component zeroth-order regular approximation, and the influence of spin-orbit coupling on involved molecular orbitals is studied, which allows for a thorough understanding of the underlying mechanisms.

Relativistic and QED corrections to one-bond indirect nuclear spin-spin couplings in X$_2^{2+}$ and X$_3^{2+}$ ions (X = Zn, Cd, Hg)

The indirect spin-spin coupling tensor, $\bm J$, between mercury nuclei in systems containing this element can be of the order of few kHz and one of the largest measured. We analysed the physics behind the electronic mechanisms that contribute to the one- and two-bond couplings $^n \bm{J}_{\mathrm{Hg}-\mathrm{Hg}}$ ($n=1, 2$). For doing so, we performed calculations for $J$-couplings in the ionized $X_2^{2+}$ and $X_3^{2+}$ linear molecules ($X$ = Zn, Cd, Hg) within polarization propagator theory, using the random phase approximation and the pure zeroth--order approximation with Dirac--Hartree--Fock and Dirac--Kohn--Sham orbitals, both at four-component and ZORA levels. We show that the ``paramagnetic-like' mechanism contribute with more than 99.98\% to the total isotropic value of the coupling tensor. By analyzing the molecular and atomic orbitals involved in the total value of the response function, we find that the $s$-type valence atomic orbitals have a predominant role in the description of the coupling. This fact allows us to develop an effective model from which QED effects on $J$-couplings in the aforementioned ions can be estimated. Those effects were found to be within the interval $(0.7;~1.7)$\% of the total relativistic effect on isotropic one-bond $^1\bm{J}$ coupling, though ranging those corrections between the interval $(-0.4;~-0.2)$\% in Zn-containing ions, to $(-1.2;~-0.8)$\% in Hg-containing ions, of the total isotropic coupling constant in the studied systems. The estimated QED corrections show a visible dependence on the nuclear charge $Z$ of each atom $X$ in the form of a power-law proportional to $Z_X^5$.

Explorations of Magnetic Properties of Noble Gases: The Past, Present, and Future

In recent years, we have seen spectacular growth in the experimental and theoretical investigations of magnetic properties of small subatomic particles: electrons, positrons, muons, and neutrinos. However, conventional methods for establishing these properties for atomic nuclei are also in progress, due to new, more sophisticated theoretical achievements and experimental results performed using modern spectroscopic devices. In this review, a brief outline of the history of experiments with nuclear magnetic moments in magnetic fields of noble gases is provided. In particular, nuclear magnetic resonance (NMR) and atomic beam magnetic resonance (ABMR) measurements are included in this text. Various aspects of NMR methodology performed in the gas phase are discussed in detail. The basic achievements of this research are reviewed, and the main features of the methods for the noble gas isotopes: 3He, 21Ne, 83Kr, 129Xe, and 131Xe are clarified. A comprehensive description of short lived isotopes of argon (Ar) and radon (Rn) measurements is included. Remarks on the theoretical calculations and future experimental intentions of nuclear magnetic moments of noble gases are also provided.

Gas-phase 21 Ne NMR studies and the nuclear magnetic dipole moment of neon-21

Gas-phase ²¹ Ne nuclear magnetic resonance spectra were measured at the natural abundance of ²¹ Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B₀ = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the ²¹ Ne nuclear magnetic moment, μ(²¹ Ne) = 0.6617774(10) μ_N . The present value of μ(²¹ Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(²¹ Ne).