Compressibility of a polydiacetylene crystal under hydrostatic pressure and reinterpretation of the pressure-effect on the 2 eV transition

Abstract

Linear and volume compressibilities for PTS crystallites under hydrostatic pressure up to 16.5 kbar are reported. Values for κ a κ o κ B and κ V are of the magnitude expected for a molecular crystal. The results are used to reinterpret literature data on the pressure-induced red shift of the 2 eV electronic transition in terms of the exciton model. It is concluded that for the lowest PTS singlet state the gas-to-crystal shift term D is about 2000 cm −1.