Zero-Magnon Lines in MnF2

The zero-magnon lines for the transition 6 A 1 → 4 T 1 in anti-ferromagnetic MnF 2 are studied in the framework of the crystal field theory, including the field of orthorhombic symmetry, the spin-orbit interaction, and the exchange interaction in the form of an effective magnetic field. It is discussed that, although the argument of Dietz. Misetich and Guggencheim seems to be effectively correct, the inclusion of the vibronic interaction is necessary for the correct understanding of the microscopic origin of the zero-magnon lines.