Fragmentation And Cooling Of Doubly Charged Anthracene Studied In An Electrostatic Storage Ring

The cooling of anthracene dications (C14H10)(2+) has been studied in a time range of 10 ms. Intact (C14H10)(2+) ions were produced in a Nanogan electron cyclotron resonance (ECR) ion source and stored in a compact electrostatic ion storage ring, the Mini-Ring. The internal energy distribution of the stored dications was probed every millisecond during the storage time using optical parametric oscillator (OPO) nanosecond laser pulses. The wavelength of the laser was tuned at 560 nm (2.214 eV), which is the center of a broad resonance peak attributed to the S-2-S-0 transition of (C14H10)(2+). The fast decay of neutral fragment counts due to laser induced dissociation was recorded for several probing times. These experimental neutral decay curves were reproduced by a model that accounted for the slow evolution of the internal energy distribution of the stored ions due to dissociation and radiative cooling processes. From the simulated internal energy distributions, we have estimated an energy shift rate varying from 140 to 30 eV/s in the time range from 1 to 9 ms, which was attributed mainly to the radiative cooling due to delayed electronic transitions. The electronic fluorescence rate was estimated to 331 s(-1) for an internal energy of 7 eV, which was similar to the electronic fluorescence rate of an anthracene cation at the same energy. We conclude that, for anthracene, the fluorescence cooling process is not sensitive to the charge of the molecule for low charge states, cation and dication.