Optical selection rules and magnon assignments for the low temperature magnetic spin structures of CsCoCl3 and CsNiCl3

The optical selection rules for excitons, magnons and exciton-magnon coupled modes are derived for the various magnetic phases of CsCoCl₃ and CsNiCl₃. For CsCoCl₃, these selection rules are used in conjunction with the energy levels calculated in the previous paper (I) to account for the sharp side bands observed in the optical spectrum. For CsNiCl₃, the discussion focuses on the utility of the selections rules to be used as a tool to distinguish phases, particularly in the region of the controversial intermediate phase.