Physics of the rotation of a PAH molecule in interstellar environments

The polycyclic aromatic hydrocarbon (PAH) molecules have recently been proposed as an important component of the ISM. The rotation of these molecules may have several observational consequences, and we aim to establish the physics of their motion. First, the physical conditions in the environment of PAHs are reviewed or computed for both cases of a reflection nebula and of the diffuse interstellar medium; specially the fluxes of the absorbed and emitted photons, and their energy are evaluated. We then examine, from a statistical point of view, the different interactions with the interstellar environment that give rise to an exchange of angular momentum