Orbital angular momentum crystal field theory

The explanation of quenching of orbital angular momentum on the basis of crystal field theory ... 

Transitions occur mainly by an electric dipole mechanism. Such transitions are allowed if the initial and final states are made up of orbitals of opposite parity (A/ =1,3,... / orbital angular momentum quantum number) and if the spin remains unchanged AS = 0) (Laporte rules, see Ligand Field Theory Spectra. However parity-forbidden transitions can occur as a result of mixing with states of opposite parity. Mixing of states by the crystal field requires that the cationic site lacks an inversion center. If the site is centrosymmetric, transitions can nevertheless be observed owing to vibronic coupling. Their probability is low and increases with temperature. 

Fig. 3. Ti(urea)gl3 single crystal. Temperature dependence of P and Px- The solid curves are the smoothed experimental data, the dashed line is calculated for py, the dotted line is calculated for pj, from the theory for the term with Dg = 1700cm" J=-600cm fc = 0.45, A = 75cm" , C7 g < 50 cm fc is the orbital angular momentum reduction factor, A is the splitting of the term, 17 q is a trigonal ligand field parameter [73F6].

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