Spectroscopic investigation of orientational disorder in an acenaphthylene molecular crystal

Abstract

AbstractThe electronic absorption spectra of an acenaphthylene single crystal are obtained in polarized light at 4.2 to 300 K. The temperature dependence of band width, maximum and integral intensity of the lowest singlet‐singlet transition at v = 21762 cm−1 are discussed. Both the band broadening of the exciton doublet with va = 21260 cm−1 and vb = 21280 cm−1 and its intensity decrease are shown to be due to a change of orientational disorder, when approaching the orientational phase transition at T = 130 K. The constancy of Davydov splitting Δ = 20 cm−1 with temperature is associated with inter‐ordering of two sets of translationally non‐equivalent acenaphthylene molecules, which does not influence the value of resonance interaction between the pair molecules.