Abstract
Fast population decay of naphthalene cations (C10H8+) has been observed in a compact electrostatic storage ring, the Mini-Ring, up to 5 ms. Laser induced dissociation due to single-photon absorption was used to probe the internal energy distribution (IED) of the stored molecular ions as a function of the storage time. To determine the energy distribution of naphthalene cations, the experimental neutral decay curve was analysed with a model including the competition between dissociation and radiative cooling. Fast cooling rates from about 70 s−1 at the internal energy 5.6 eV to 140 s−1 at 6.2 eV were measured and compared with the data in the literature. This fast cooling mechanism is attributed to the fluorescence from thermally excited electrons and may have important implications in astrophysics for the lifetime and the critical size of Polycyclic Aromatic Hydrocarbons (PAH) in the interstellar medium.
Highlights
The abundant presence of Polycyclic Aromatic Hydrocarbons (PAH) in the interstellar medium was proposed almost thirty years ago [1, 2] in order to explain the unidentified infrared (UIR) emission band
We study the cooling of naphthalene cations stored in our small electrostatic storage ring, the Mini-Ring
The measurements were performed using a small electrostatic storage ring and laser induced dissociation to probe the evolution of the internal energy distribution (IED) of the stored molecular ions from 0.5 to 4.5 ms storage time
Summary
The abundant presence of PAHs in the interstellar medium was proposed almost thirty years ago [1, 2] in order to explain the unidentified infrared (UIR) emission band. A numerical method is used to analyze the experimental data in order to determine the population decay rates of the stored ions for several excitation energies.
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