Bond Dissociation Energies in Heavy Element Chalcogen and Halogen Small Molecules

Thermodynamic properties including bond dissociation energies (BDEs), heats of formation, and gas-phase acidities for the hydrides and dimers of chalcogens and halogens, H2Y, HX, Y-2, and X-2 for Y = Se, Te, and At and X = Br, I, and At, have been predicted using the Feller-Peterson-Dixon composite-correlated molecular orbital theory approach. A full four-component CCSD(T) approach was used to calculate the spin-orbit effects on thermodynamic properties, except for Se-2, where the AoC-DHF value was used due to strong multireference effects in Se-2 for the SO calculations. The calculated results show that the At-2 BDE is quite small, 19.5 kcal/mol, with much of the low bond energy due to spin-orbit effects. H2Po is not predicted to be stable to dehydrogenation to Po + H-2 in terms of the free energy at 298 K. In the gas phase, HAt is predicted to be a stronger acid than H2SO4. The current results provide insights into potential difficulties in the actual experimental observation of such species for heavy elements.

Automated summary

Thermodynamic properties of chalcogens and halogens hydrides and dimers were predicted using a composite-correlated molecular orbital theory approach. The results showed that At-2 has a small bond dissociation energy and H2Po is unstable to dehydrogenation. HAt was predicted to be a stronger acid than H2SO4 in the gas phase.