Diatomic molecules between very heavy elements of group 13 and group 17: Astudy of relativistic effects on bonding

The effects of relativity on the bonding between heavy elements of groups 1 3 and 17 have been investigated. Using extensive energy minimized basis set s, calculations have been carried out within several models which include r elativistic effects at various levels-4-component Dirac-Hartree-Fock, spin- free relativistic, Levy-Leblond, mass-velocity-Darwin perturbation theory, as well as nonrelativistic Hartree-Fock calculations. The relativistic effe cts on spectroscopic constants are dramatic, and dominated by the spin-orbi t splitting and the relativistic contraction of the valence p-orbitals. Par ticularly noteworthy is the spin-orbit induced change of sign of the dipole moment for [113][117]. This highlights the importance of including the spi n-orbit effect in the variational optimization of the wave function for hea vy elements. (C) 2001 American Institute of Physics.