Synthetic rotational profiles of emission and absorption bands of interstellar polycyclic aromatic hydrocarbons

The spectrometers on board Herschel are likely to be able to detect far-IR emission bands from interstellar PAHs, possibly resolving their rotational envelopes. For some specific PAHs we calculated synthetic rotational profiles of their low-energy vibrational modes and of their low-lying permitted electronic transitions, for comparison respectively with the forthcoming Herschel observations and high resolution spectra of Diffuse Interstellar Bands. Such profiles were obtained through a Monte-Carlo model of the photo-physics of isolated interstellar PAHs, whose molecular properties were calculated using state-of-the-art quantum-chemical techniques. Upon successful identification of specific PAHs, comparison with observations will provide both useful information on the physical environment in which the molecule is embedded and be an indirect measurement of molecular parameters which are very difficult to obtain either theoretically or in terrestrial laboratories.