ABSTRACT
We present new experimental results on thermal and ion irradiation processing of frozen ammonia-carbon dioxide mixtures. Some mixtures were deposited at low temperatures (T ≈ 16 K). Upon warming up to 160 K, complex chemical reactions occur leading to the formation of new molecules and, in particular, of ammonium carbamate. We also show that the same species are produced when water is the dominant species in the ternary mixture with ammonia and carbon dioxide. The samples have been irradiated with 144 keV S(9+) ions at 16 K and 50 K. Also in this case, new chemical species are formed as e.g. ammonium formate, CO and OCN(-). The results are discussed in the light of their relevance to the chemical evolution of ices in the interstellar medium and in the solar system. In particular, we suggest searching for them among the gas phase species sublimating from grains around young stellar objects and from the cometary nuclei approaching the Sun.
ABSTRACT
An innovative experimental equipment allowing to study the sputtering induced by ion beam irradiation is presented. The sputtered particles are collected on a catcher which is analyzed in situ by Auger electron spectroscopy without breaking the ultra high vacuum (less than 10(-9) mbar), avoiding thus any problem linked to possible contamination. This method allows to measure the angular distribution of sputtering yield. It is now possible to study the sputtering of many elements such as carbon based materials. Preliminary results are presented in the case of highly oriented pyrolytic graphite and tungsten irradiated by an Ar(+) beam at 2.8 keV and 7 keV, respectively.
