Modification of vibrational selection rules in the photoinduced spin-crossover phase

We show that vibrational selection rules are modified in the nonequilibrium photoinduced phase in the single-crystalline spin-crossover complex [Fe(pic)₃]Cl₂EtOH. In the Raman spectra, several infrared-active modes, forbidden by the selection rules in the thermally induced phase, appear in the photoinduced phase. In addition, these Raman lines are enhanced significantly as a result of resonant excitation to the intramolecular transition of the ligand molecule. These results indicate that the ligand molecule should be deformed drastically and the local symmetry breaks in the photoinduced phase.