The quadrupole moment of the 3 2+ nuclear ground state of Au197 from electric field gradient relativistic coupled cluster and density-functional theory of small molecules and the solid state

Abstract

An attempt is made to improve the currently accepted muonic value for the 197Au nuclear quadrupole moment f+0.547s16d310−28 m2g for the 3/2+ nuclear ground state obtained by Powers et al. fNucl. Phys. A230, 413 s1974dg. From both measured Mössbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60310−28 m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the 197Au isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the 197Au nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples fCCSDsTd level of theoryg for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSDsTd procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers fInorg. Chem. 40, 6123 s2001dg a significantly enhanced 197Au nuclear quadrupole coupling constant in sCOdAuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSDsTd calculations finally give a nuclear quadrupole moment of +0.64310−28 m2 for 197Au. It is argued that it is currently very difficult to improve on the already published muonic value for the 197Au nuclear quadrupole moment.