Heat capacity prediction for polynuclear aromatic solids using vibration spectra

Heat capacity, at constant pressure and volume, are important thermodynamic parameters for solids. Cp is accessible experimentally, from near 0 K to the melting point, while CV is more accessible by computation. The connection between heat capacity and internal energy and entropy, the generation of solid-fluid phase diagrams and its close relation to molecular structure and atomic scale vibrations are well known. Thus, heat capacity has many direct uses and also has the potential to provide insights into the structure, mean molar mass, and phase behavior of poorly defined aromatic hydrocarbon fractions of industrial interest such as vacuum residues and asphaltenes that are not otherwise available. Infrared, far infrared, Raman and photo acoustic spectra are readily obtained experimentally. However, technical restrictions related to the detection and characterization of such spectra for polynuclear aromatic compounds limit the development of models for predicting heat capacity using experimental vibration spectra. In this paper, two approaches, one relying primarily on experimental spectra, and one based on direct calculation of spectra using density functional theory are presented and their potential for application discussed.