Intramolecular anharmonicity in the naphthalene molecule: thermodynamics and spectral effects.

The anharmonicity of the ground electronic state of the naphthalene molecule has been investigated using a tight-binding potential energy surface model. The vibrational density of states is calculated from a mixed classical quantum theoretical approach. The primary assumption of this model is that the evolution of the mean anharmonic quantum energy as a function of temperature follows the classical evolution. From the thermal expansion of the classical free energy obtained using a reversible-scaling method, the mean vibrational frequency has also been determined as a function of temperature.