Infrared spectroscopy of gas-phase PAH molecules. I. Role of the physical environment.

Abstract

In the PAH model, polycyclic aromatic hydrocarbons are responsible for the Unidentified IR (UIR) bands observed in emission in many astronomical objects. Although this model states that these molecules are isolated, and at high temperatures (T ∼ 1000 K), most laboratory spectra have been obtained for condensed molecules at low temperatures. In this paper, we present the IR absorption spectra (3-20 μm), measured for gas phase molecules at high temperatures. For the three studied species, pyrene (C 16 H 10 ), coronene (C 24 H 12 ), and ovalene (C 32 H 14 ), these spectra are compared to those obtained in condensed phases, solid state and rare gas matrices. The relative band intensities clearly depend on the molecular environment