text: In case (c), the spin-orbit coupling is stronger than the coupling to the internuclear axis, and  and  from case (a) cannot be defined.  Instead  and  combine to form , which has a projection along the internuclear axis of magnitude .  Then , as in case (a).
  The good quantum numbers in case (c) are , , and . Since  is undefined for this case, the states cannot be described as ,  or . An example of Hund's case (c) is the lowest Π state of diiodine (I), which approximates more closely to case (c) than to case (a).
  The selection rules for ,  and parity are valid as for cases (a) and (b), but there are no rules for  and  since these are not good quantum numbers for case (c).