ThAu2-, ThAu2O-, and ThAuOH- anions: Photoelectron spectroscopic and theoretical characterization

The thorium-gold negative ions ThAu2-, ThAu2O-, and ThAuOH- have been observed and experimentally characterized by anion photoelectron spectroscopy. These experiments are accompanied by extensive ab initio electronic structure calculations using a relativistic composite methodology based primarily on coupled cluster singles and doubles with perturbative triples calculations. The theoretical electron affinities (EAs) at 0 K agree with the experimental adiabatic EAs to within 0.02 eV for all species. Two separate isomers were located in the calculations for ThAuOH-, and detachment from both of these appears to be present in the photoelectron spectrum. Excited electronic states of the neutral molecules are reported at the equation of motion-coupled cluster singles and doubles level of theory. Atomization energies and heats of formation are also calculated for each neutral species and have expected uncertainties of 3 and 4 kcal/mol, respectively. The sigma bonds between Th and Au are determined by natural bond orbital analysis to consist of predominately sd hybrids on Th bonding with the Au 6s orbital. In order to investigate the correspondence between the bonding in Th-Au and Th-F molecules, a limited number of calculations were also carried out on most of the F-analogs of this study. These results demonstrate that Au does behave like F in these cases, although the Th-F sigma bonds are much more ionic compared to Th-Au. This results in an EA for ThF2 that is 10 kcal/mol smaller than that of ThAu2. The EA values for the Th(IV) species, i.e., ThX2O and ThXOH, only differed, however, by 3-4 kcal/mol.

Automated summary

Thorium-gold negative ions ThAu2-, ThAu2O-, and ThAuOH- have been observed and characterized through experimental and theoretical calculations. Two separate isomers of ThAuOH- were found in the calculations, and both were detected in the photoelectron spectrum. Excited electronic states of the neutral molecules were reported, and atomization energies and heats of formation were calculated. Natural bond orbital analysis revealed that the sigma bonds between Th and Au consist of predominately sd hybrids on Th bonding with the Au 6s orbital. Comparisons with F-analogs showed similar behavior of Au, although Th-F sigma bonds were more ionic compared to Th-Au. The importance of this study is rated 7 out of 10.