Measurement of recurrent fluorescence cooling rates of PAH cations and di-cations using a compact electrostatic storage ring, the Mini-Ring
J. Bernard1, A. Al-Mogeeth1, C. Joblin2, and S. Martin1
1Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon,
69622 Villeurbanne cedex, France
2Universite de Toulouse, UPS-OMP, IRAP, Toulouse, France
Email: jerome.bernard@univ-lyon1.fr
A very compact electrostatic ion storage ring, so-called Mini-Ring, has been built in Lyon almost ten years ago1. The design uses the focusing properties of conical shaped electrostatic mirrors to reduce the total number of necessary electrodes to 10 only. Compared to other existing storage rings at that time of several meters of circumference, it deserved its name of Min-Ring because its size was restraint to fit on a single plate 400 mm×200 mm.
With this Mini-Ring, we have thoroughly studied and quantified the radiative cooling of PAH cations (Naphthalene, Anthracene, Pyrene) and di-cation (Anthracene only). We have evidenced a fast radiative cooling that cannot be attributed to infrared vibrational emissions only. This fast radiative cooling, referred now as recurrent fluorescence, involves a mechanism that had been predicted in the early 80s, i.e., the transient population of electronic excited states from high vibrational states of the ground state of “hot” PAH cations via the inverse process of internal conversion (IIC). This IIC process is rapidly followed by a visible photon emission taking away few eVs from the system at once. The previous studies on singly charged PAHs2,3 has been recently extended to di-cations of Anthracene. An average energy shift rate of about 50 eV/s has been measured for di-cation, two times less compared to cation.
References:
1. Bernard, J. et al. A “tabletop” electrostatic ion storage ring: Mini-Ring. Rev. Sci. Instrum. 79, 075109 (2008).
2. Martin, S. et al. Fast Radiative Cooling of Anthracene Observed in a Compact Electrostatic Storage Ring. Phys. Rev. Lett. 110, 063003 (2013).
3. Martin, S. et al. Fast radiative cooling of anthracene: Dependence on internal energy. Phys. Rev. A 92, 053425 (2015).