In this paper we will present a study of several Tm and Pr compounds, where
the rare earth atoms have as their two lowest energy levels a quasi-doublet
ground state. These compounds are also compared with Er and/or Dy
compounds, which have a Kramers doublet as ground state. Four compounds
(TmNi5, TmCu2, TmCuAl and
PrRu2Si2) are discussed in
sequence, where the energy separation of the two levels of the quasi-doublet
ground state doublet is increasing. These compounds were studied with rare
earth Mössbauer spectroscopy and µSR as the main measuring
techniques.