Temperature Dependence of the Entropy and the Heat Capacity Calculated from the Raman Frequency Shifts for Solid Benzene, Naphthalene and Anthracene

Abstract

Temperature dependences of the free energy (F), entropy (S) and the heat capacity (C_v) are calculated (P=0) for the organic compounds (solid benzene, naphthalene and anthracene) by using the quasiharmonic approximation. Contributions to those thermodynamic functions due to the Raman frequencies of lattice modes (solid benzene), librational modes (naphthalene), phonons and vibrons (anthracene) are taken into account in our calculations. We obtain that similar linear increase of F and nonlinear increase of S and C_v, occur with the increasing temperature in benzene and naphthalene. This linear (F) and nonlinear (S, C_v) increase is rather different for anthracene as the molecular structure becomes complex (benzene-naphthalene-anthracene), as expected. Our calculations by the quasiharmonic approximation can be compared with the experiments for those organic compounds.