High-resolution infrared absorption spectroscopy of thermally excited naphthalene. Measurements and calculations of anharmonic parameters and vibrational interactions.

We report in this paper the recording and analysis of the vibrational spectrum of naphthalene in the 1.6-200 microm (50-6000 cm(-1)) spectral range with a resolution of 0.005 cm(-1). The spectrum, recorded at room temperature, shows several complex structures in the Q branches of the c-type bands, which can be assigned to hot-band sequences as well as combination bands and overtones. To analyse the experimental data, we developed a model based on anharmonic calculations which predicts the transitions (positions and intensities) involving the vibrational levels populated at room temperature. This work permits us to estimate the validity and limitations of our calculations, which can be used to predict the band profiles of naphthalene (and larger PAHs) at various temperatures, with potential astrophysical applications.