Fast radiative cooling of anthracene was observed in a compact electrostatic storage ring by probing the evolution of the internal energy distribution of a stored (C(14)H(10))(+) molecular ensemble via laser excitation. We have measured the mean radiative decay rate to be about 120 to 250 s(-1) for internal energies in the range from 6.6 to 6.8 eV. Such a high decay rate is 2 orders of magnitude larger than the infrared emission cooling rate expected for vibrational transitions. It is attributed to fluorescence from thermally excited electrons. This fast cooling mechanism may have important implications in astrophysics concerning the lifetime and the critical size of polycyclic aromatic hydrocarbons in interstellar conditions.

The low-energy sputtering of boron nitride, magnesium oxide, boron nitride and aluminum nitride ͑BNAlN͒, and boron nitride and silicon oxide (BNSiO 2 ) by xenon ions of bombarding energies 350, 500 eV, and 1 keV was studied experimentally. In order to measure the ion current without being significantly disturbed by slow ions, only planar probes were used during short duration sputtering experiments ͑of the order of 10 h͒. Moreover, slow ion current contribution was estimated by numerical simulations and subtracted from each ion current measurement. It was found that the ion-beam incidence effect on sputtering yields was not as important as for theoretical results or experimental results on quasinonrough solid surfaces, for which it is possible to observe a more pronounced angular dependence of the sputtering yield. This phenomenon is due to surface irregularities of ceramic materials and because of surface roughness the macroscopic sputtering yield should actually result from the convolution of the microscopic sputtering yield by the angular distribution of surface facet incidences. The irregular surface structure of ceramics like BNSiO 2 or BNAlN seems to be sputtered differently due to a differential erosion from grain to grain and from grain to surrounding matrix. This uneven erosion may be explained by the wide angular distribution of facet incidences of surface microprofiles and the various binding energies in the selvage of material. Finally, the dependence of sputtering yield at normal incidence on ion energy, in the range 0.35-1 keV, is almost a linear one.

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