Knowledge Bank

A brief review will be given of the spectra of hydrated ions of the first transition group. It is shown that the gross features of the spectra of the ions are fairly well explained by crystal field theory. Details of the structure of the absorption bands of some of the salts were studied by using low temperatures, single crystals, and polarized light. The results for $CuSO4.5H2O$ and $NiSO4.7H2O$ lead to a determination of the crystal field parameters not only for the cubic but also for the tetragonal components. The transitions were also shown to be electric dipole transitions, made allowed by vibrations. The vibrations permitting the transitions are in the range from 150 to $300cm-1$. Combining the optical spectra with data on the anisotropy of the g-factors of the ground state leads to the requirement of a smaller spin-orbit coupling constant than in the free ion. This is interpreted as evidence for spreading of the d-orbitals over the surrounding water molecules.