Thermomodulation Study of 0–0 Exciton Absorption Bands in Anthracene

Abstract

Thermoreflectance spectra in the lowest singlet-singlet transition region of anthracene have been measured at liquid nitrogen temperature. The derivative optical constants are obtained by the Kramers-Kronig analysis of the spectra. The asymmetric broadening of the b-polarized 0–0 exciton absorption band with temperature is suggested. The frequency of the K=0 polariton for the 0–0 absorption band has been confirmed to be located at 25484 cm⁻¹ and at 25497 cm⁻¹ in the a- and the b-polarized spectra respectively. The K=0 polariton-exciton splittings for the a- and b-polarization are respectively 77 cm⁻¹ and 378 cm⁻¹, whose magnitudes are proportional to the oscillator strength of the respective 0–0 absorption band. The b-polarized thermoreflectance spectrum at liquid helium temperature has also been measured and discussed briefly.