Fragmentation and cooling of doubly charged anthracene studied in an electrostatic storage ring

Abstract

The cooling of anthracene dications (C 14 H 10 ) 2+ has been studied in a time range of 10 ms. Intact (C 14 H 10 ) 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 (C 14 H 10 ) 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.

Radiative cooling of size-selected gas phase clusters

“…Gas phase experiments performed in a storage ring device, mimicking the conditions encountered by this molecule in the outer space, have shown that a beam of (C 14 H 10 ) + cools down radiatively at rates of around 200 s −1 upon laser excitation. These rates are two orders of magnitude higher than those expected from vibrational transitions, thus suggesting transitions of electronic nature via the RF mechanism [102][103][104][105].…”

A new technique for measurement of subrotational lifetime of molecular ions

“…On the other hand experimental measurements of these lifetimes report values in the range of several nanoseconds to few milliseconds or higher. Lifetime measurements in the range of microseconds to seconds have been traditionally carried out using storage rings [11][12][13] and translational energy spectroscopy 14 . With the advent of multi-particle coincident time-of-flight measurements, lifetimes for a variety of molecular ions were reported [15][16][17] primarily in the range of nanoseconds.…”

Decay Dynamics in Molecular Beams

“…These aspects are by now well established experimentally, primarily by work at ion storage rings (Andersen et al, 1996(Andersen et al, , 2001Hansen et al, 2001;Tomita et al, 2001;Andersen et al, 2003a;Andersen, Heber, & Zajfman, 2004;Fedor et al, 2005;Toker et al, 2007;Froese et al, 2011;Lange et al, 2012;Toker et al, 2012;Martin et al, 2013;Menk et al, 2014;Martin et al, 2015;Breitenfeldt et al, 2016;Hansen et al, 2017b;Ji et al, 2017;Martin et al, 2017;Anderson et al, 2018;Bernard et al, 2019;Martin et al, 2019), occasionally in a form where other channels are present, but also at single pass devices such as time-offlight mass spectrometers (Hansen & Campbell, 1996;Hansen & Echt, 1997;Ferrari et al, 2015;Hansen et al, 2017a;Ferrari et al, 2018a, b), and here the focus will be on the theoretical aspects.…”