Predicted fluorescence mechanism in highly isolated molecules: The Poincaré fluorescence

We predict a completely new behavior of fluorescence for large- or intermediate-size molecules which are highly isolated (e.g., in the interstellar medium). After a uv absorption, the energy decay by ir-emission alone is very slow ({}3 s). The system evolves at constant energy during a long time period in its phase space, and unusual phenomena can occur. We infer an inverse internal conversion and a resulting recurrent fluorescence that we propose to name Poincar\'e fluorescence. Such a behavior seems quite universal and has characteristics markedly different from the usual fluorescence.