Two-component spin–orbit calculations for the hetero diatomic molecules TlAt and (1 1 3)(1 1 7) with relativistic effective core potentials

Bond lengths, harmonic vibrational frequencies and dissociation energies of TlAt and (1 1 3)(1 1 7) are calculated at the highly correlated level of theory with and without spin–orbit interactions. Spin–orbit effects of Group 13 and Group 17 elements almost cancel out for Re. The spin–orbit effects on De of TlAt(−1.20 eV) and (1 1 3)(1 1 7)(−2.05 eV) are roughly the sum of those of the corresponding element hydrides. Element 113 becomes more electronegative than Element 117 upon inclusion of spin–orbit interactions in the (1 1 3)(1 1 7) molecule. Electron correlations and spin–orbit effects are almost additive in the TlAt molecule, but the nonadditivity is quite pronounced for the (1 1 3)(1 1 7) molecule.