The term splitting of the absorption spectrum of thulium sulphate octalhydrate due to crystal field effects was calculated according to first order perturbation theory. Departures from Russell-Saunders Coupling were taken into account. The various transition mechanisms were examined with and without crystal coupling. It was found that crystal coupling effects are important in destroying J and parity selection rules. Transitions induced by these effects are often more important than transitions calculated neglecting crystal coupling. Zeeman patterns were also studied for the several interesting directions of propagation and polarization of the light relative to the magnetic field directione Susceptibility calculations made for thulium, praseodymium and neodymium sulphate octahydrate indicate field calculations cannot always be made neglecting all but nearest neighbor contributions.
Paskin, Arthur and Keller, J. M., "Adsorption spectrum of thulium sulphate octahydrate" (1953). Ames Laboratory ISC Technical Reports. 56.