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Quantifying the effect of anharmonicity on the infrared spectrum of largemolecules such as polycyclic aromatic hydrocarbons (PAHs) at high temperatureis the focus of a number of theoretical and experimental studies, many of themmotivated by astrophysical applications. We recorded the infrared spectrum ofpyrene C16H10 microcrystals embedded in a KBr pellet over a wide range oftemperature (14 -723 K) and studied the evolution of band positions, widths andintegrated intensities with temperature. We identified jumps for some of thespectral characteristics of some bands in the [423- 473]K range. These wereattributed to a change of phase from crystal to molten in condensed pyrene,which appears to affect more strongly bands involving large CH motions.Empirical anharmonic factors that describe the evolution of band positions andwidths with temperature were retrieved from both phases over an unprecedentedtemperature range. The derived values were found to be consistent withavailable gas-phase data. We provide recommended values for anharmonic factorsand conclude about the interest of the methodology to provide data of interestfor comparison with theoretical models and as inputs of models that simulatethe infrared emission of astro-PAHs.

Experimental Approach to the Study of Anharmonicity in the Infrared Spectrum of Pyrene from 14 to 723 K