Nuclear volume effects in equilibrium stable isotope fractionations of mercury, thallium and lead

Abstract

The nuclear volume effects (NVEs) of Hg, Tl and Pb isotope systems are investigated with careful evaluation on quantum relativistic effects via the Diracâ €™ s formalism of full-electron wave function. Equilibrium 202 Hg/ 198 Hg, 205 Tl/ 203 Tl, 207 Pb/ 206 Pb and 208 Pb/ 206 Pb isotope fractionations are found can be up to 3.61‰, 2.54‰, 1.48‰ and 3.72‰ at room temperature, respectively, larger than fractionations predicted by classical mass-dependent isotope fractionations theory. Moreover, the NVE can cause mass-independent fractionations (MIF) for odd-mass isotopes and even-mass isotopes. The plot of vs. for Hg-bearing species falls into a straight line with the slope of 1.66, which is close to previous experimental results. For the first time, Pb 4+ -bearing species are found can enrich heavier Pb isotopes than Pb 2+ -bearing species to a surprising extent, e.g., the enrichment can be up to 4.34‰ in terms of 208 Pb/ 206 Pb at room temperature, due to their NVEs are in opposite directions. In contrast, fractionations among Pb 2+ -bearing species are trivial. Therefore, the large Pb fractionation changes provide a potential new tracer for redox conditions in young and closed geologic systems. The magnitudes of NVE-driven even-mass MIFs of Pb isotopes (i.e.,) and odd-mass MIFs (i.e.,) are almost the same but with opposite signs.