Energetic ion irradiation of N2O ices relevant for Solar system surfaces

Ices are the dominant surface material of many Solar system objects, such as comets and trans-Neptunian objects. They are continuously exposed to ion bombardment by solar wind ions and cosmic rays, which trigger secondary ion emission, contributing to the exosphere formation. Laboratory studies demonstrated the effects of energetic processing of ices at low temperature, showing the production of molecules and free radicals of astrophysical interest. Nitrous oxide (N2O) is one of the molecular species observed in star-forming sites, reason why it may be present in the ices covering some minor bodies in the outer Solar system. In the current work, N2O ice at 10 K was irradiated by energetic (MeV/u) multicharged heavy ions (e.g. Rh-105 and Ba-140); the sputtered species were detected and analysed by the TOF-PDMS technique (time-of-flight plasma desorption mass spectrometry). Small positive and negative secondary ions were identified: N+, N-2(+), NO+, O+, and O-. The bombardment also induces production of ion cluster series: (N-2)(n)R-m(+), (NO)(n)R-m(+), (N2O)(n)R-m(+), where R = N+, N-2(+), NO+, N2O+, O-m(+) (n up to similar to 10, m = 1-3). Their yield distributions follow the sum of two decreasing exponentials, one fast -F and another slow -S, suggesting a two-regime formation. Most of the yield distributions have the same pair of exponential decay constants, around k(F) similar to 1.4 and k(S) similar to 0.15 u(-1). Based on this behavior, an emission description for aggregates is proposed, useful to understand the processes by which neutral and ionized molecular species are delivery to the gas phase in space.

Automated summary

Ices are dominant surface materials for many Solar system objects, continuously exposed to ion bombardment triggering exosphere formation. Laboratory studies show energetic processing of ices at low temperatures can produce molecules and free radicals of astrophysical interest. Irradiating N2O ice with high-energy multicharged heavy ions led to the detection of various sputtered species and ion cluster series.