Swmmavy. The electron transfer spectra 01 adducts of the tide metal halides with a series of ligands (aitriles, dialkylchalcogenides, phosphoryl and thiophosphoryl ligands and phosphincs) have been studied. The effect of halogen substitution on the halogen metal transitions is discussed by comparing thc spectra of the adducts with those of the hexahalometalates. The origin of the two ligand-metal transitions observed in most adducts is discussed and the splitting of the metal d levels in these aImost octahedral adducts is estimated. For each motal halide, the series of adducts with dialkyl chalcogenides show a linear relationship of slope one between the ligand ionisation potentid and the ligand-metal charge transfer cnergy. Tho ligand pptical electronegativities have been estimated.