Resonance Raman spectrum of the I−3 ion and the phase transition in the organic metal TMAITCNQ

Resonance Raman spectra of single crystals of the organic metal TMAITCNQ exhibit strong resonances from the 1^?₃ ions. Overtones up to υ = 5 were readily observed. Temperature-dependent measurements reveal a sharp discontinuity of the fundamental intensity and of the linewidth of the first overtone at 150 K. These results indicate that the iodine ions are directly involved in the semiconductor to semiconductor phase transition which is known to occur at this temperature.