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

Abstract

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⁻.