Infrared absorption and reflection studies of organic radical salt: K ⁺TCNQ^-

The bulk reflectivity and absorption (using alkali halide matrices and thin film dispersions) of polycrystalline K⁺TCNQ^- in the wavelength range between 30 and 4000 cm^-1 have been examined in detail. The sharp reflectivity peaks have been analyzed using a classical oscillator fitting procedure to give the peak and oscillator parameters. Most of the observed infrared peaks have been assigned to the fundamental modes of TCNQ^- and lattice vibrations. The temperature dependence of the CN stretching peaks in particular have been studied in the 300-433°K temperature range. The reversible and gradual disappearance of one set of CN stretching peaks in K⁺TCNQ^- has been tentatively linked to a possible cell halving phase transition at T_c∼379°K. The results are compared with the spectrum of Rb⁺TCNQ^- which is isomorphous with the postulated high temperature phase of K ⁺TCNQ^-.