Charge transfer states and optical absorption in octahedrally hydrated paramagnetic salts

A comprehensive theory is given for all observed optical absorptions which do not involve a spin-change in the paramagnetic ion. Except for the anomalous behaviour of the vanadous ion, good agreement is found between the calculated and the observed oscillator strengths. The operative mechanism in the absorption is the vibrational motion of the ligands, enabling virtual transitions to odd-parity charge transfer states to take place. In these states the central ion loses an electron to the ligands; this situation is also analysed in the paper.