Dirac-Fock One-Centre Calculations Part 8. The1Σ States of ScH, YH, LaH, AcH, TmH, LuH and LrH

Dirac-Fock one-centre expansion calculations are reported for the title molecules. The calculated bond lengths of YH, LaH and LuH are about 5% above experiment. The calculated force constants for YH and LuH are in excellent agreement with experiment. The lanthanoid contraction from LaH to LuH is calculated to be 21 pm (exp. 19) and the corresponding actinoid contraction of bond lengths from AcH to LrH 33 pm. The effective radius of Lr is only 3 pm larger than that of Lu but Ac is 15 pm larger than La. Very small relativistic effects on bond lengths and strengths are found. Trends in orbital energies and hybridizations across the Periodic Table are discussed, including an SCF lanthanoid expansion of the 5 d shell from La to Lu. The 4 d orbital energy of Y is anomalously high. This trend is termed "primogenic repulsion' by the 3 d shell.