Reactions involving polysulfides

A reaction path involving six-membered polysulfide rings was found to be much more exothermic than reduction of gold chloride by galena alone. However, at the initial stage of gold reduction, reaction rates and the importance of a reaction path involving polysulfides may be limited by the availability of Pb-polysulfide or elemental sulfur.

X-ray photoelectron (XPS) spectra were calculated for the adsorbed gold, Au-chlorides, and Au-polysulfides. All these species cause similar peak chemical shifts of the S(2p_3/2) and S(2s) XPS peaks. Therefore, it is likely that experimentally obtained and fitted XPS peaks contain varying contribution of different oxidation states and gold ligands. Calculated XPS spectra also show how the charge density distribution of adsorbate structures influences the electronic structure of the underlying substrate.

Scanning tunneling (STS) spectra were calculated for different adsorbed gold species on PbS in order to develop a tool that can help to identify which adsorbate structure is present at the surface and to study the local electronic structure of such sites. The most significant difference is the change of the local band gap which decreases from $\approx$ 1 eV for galena-Au(III)Cl₃ and about 0.5 eV for galena-Au(I)Cl to a metal-like local environment with no bandgap for elemental gold in galena-Au and galena-Au₂ (the bulk band gap of fresh galena is $\approx$ 0.4 eV). The calculated STS spectrum of galena-Au₂ was found to be very similar to STS spectra near the rim of the gold island.