The calculation of field shift effects in the rotational spectra of heavy metal-containing diatomic molecules using density functional theory: comparison with experiment for the Tl-halides and Pb-chalcogenides

The electron densities at the Tl nucleus in T1X (where X = F, Cl, Br and I) and at the Pb nucleus in PbY (where Y = O, S, Se, Te) have been calculated using density functional theory. From these quantities the molecular field shift parameter, V-01(i) (i = Pb or Tl), in each diatomic molecule may be derived. The results show a good comparison with experimental data. In the course of this work various other spectroscopic constants have been calculated for these two classes of compounds and in so doing the performance of several model Hamiltonians and basis sets has been evaluated. Using the method developed here, field shift effects in a small number of other heavy metal-containing diatomic molecules have been evaluated and a tentative explanation for the trends observed is given. (C) 2003 Elsevier B.V. All rights reserved.