Time evolution of internal energy distribution of Anthracene studied in an electrostatic storage ring, the Mini-Ring

Fast radiative cooling of polycyclic aromatic hydrocarbon (PAH) was studied by probing the time evolution of the internal energy distribution of hot molecular ensembles in the ms range. Anthracene cations (C₁₄H₁₀)⁺ prepared in an electron cyclotron resonance ion source were stored in an electrostatic storage ring, the Mini-Ring [1]. The experiment showed that in the first milliseconds, the time evolution of the stored ion population distribution was dominated by the unimolecular dissociation of the molecular ions with higher internal energy. Then, in the next milliseconds, the unimolecular dissociation was quenched by radiative cooling. In a larger time range, from 4 to 8 ms, the time evolution of the internal energy distribution was probed by reheating a part of the molecular ensemble by laser photon absorption at different storage times. We report here the measurement of a fast radiative cooling rate (100s⁻¹) that can't be explained by vibrational IR emission but rather by electronic fluorescence from thermally excited electronic states [2]