Theoretical predictions of trends in spectroscopic properties of homonuclear dimers and volatility of the 7p elements

Fully relativistic density functional theory electronic structure calculations were performed for homonuclear dimers of the 7p elements, 113-118 and their 6p homologs, Tl through Rn. All the dimers of the heaviest elements, with the exception of (118)(2), were found to be weaker bound than their lighter homologs. The difference in the dissociation energy (D(e)) between the 6p and 7p homologs was shown to decrease from group 15 to group 17, with a reversal of the trend in group 18. A remarkable feature is a shift of the maximum in D(e)(M(2)) from group 15 in the third through sixth rows to group 16 in the seventh row. Strong relativistic effects on the 7p atomic orbitals, particularly, their large spin-orbit splitting, were shown to be responsible for these trends. Using the calculated D(e)(M(2)), the sublimation enthalpies, Delta H(sub), of macroamounts, or formation enthalpies of gaseous atoms, Delta H(f)(g), of the heaviest elements were estimated using a linear correlation between these quantities in the chemical groups. The newly estimated values are in good agreement with those obtained via a linear extrapolation from the lighter homologs in the groups.