However, absorption bands are narrow, probably
because of the excitation within f level The lanthanoid ions other
than the f 
0 type (La
3+ and Ce
4+) and the f 
14 type (Yb
2+ and Lu
3+) are
all paramagnetic The first ionisation enthalpies of the lanthanoids are around
600 kJ mol
–1, the second about 1200 kJ mol
–1 comparable with those
of calcium A detailed discussion of the variation of the third ionisation
enthalpies indicates that the exchange enthalpy considerations (as in
3d orbitals of the first transition series), appear to impart a certain
degree of stability to empty, half-filled and completely filled orbitals
f level