Polarized Absorption Spectra of Single Crystals of Ion Radical Salts. III. Temperature Dependence of the Crystal Spectra of Potassium-Chloranil

Abstract

Abstract The polarized absorption spectra in the 10000–37000 cm−1 region were observed on the single crystal of the water-free modification of the potassium-chloranil salt, K+·(chloranil)−, by using a microspectrophotomer, and the variation of the spectra with temperature was examined. The crystal gives a near-infrared absorption band associated with the charge transfer between chloranil radical anions, the maximum of which is located at 11.5×103 cm−1. The absorption bands in the 20000–37000 cm−1 region were assigned to the local-excitation bands associated with the transitions in the chloranil anion. The intensity of the charge-transfer band gradually increases on lowering the temperature. An abrupt increase of intensity occurrs in the charge-transfer band at the phase-transition point. There is a close correlation between this change and the temperature dependence of the paramagnetic susceptibility of the salt.