We study the chemical evolution of H 2 O:CO:NH 3 ice mixtures irradiated with soft X-rays, in the range 250 − 1250 eV. We identify many nitrogen-bearing molecules such as e.g., OCN − , NH + 4 , HNCO, CH 3 CN, HCONH 2 , and NH 2 COCONH 2 . Several infrared features are compatible with glycine or its isomers.During the irradiation, we detected through mass spectroscopy many species desorbing the ice. Such findings support either the infrared identifications and reveal less abundant species with not clear infrared features. Among them, m/z = 57 has been ascribed to methyl isocyanate (CH 3 NCO), a molecule of prebiotic relevance, recently detected in protostellar environments.During the warm up after the irradiation, several infrared features including 2168 cm −1 band of OCN − , 1690 cm −1 band of formamide, and the 1590 cm −1 band associated to three different species, HCOO − , CH 3 NH 2 and NH + 3 CH 2 COO survive up to room temperature. Interestingly, many high masses have been also detected. Possible candidates are methyl-formate, (m/z = 60, HCOOCH 3 ), ethanediamide (m/z = 88, NH 2 COCONH 2 ), and N-acetyl-L-aspartic acid (m/z = 175). This latter species is compatible with the presence of the m/z = 43, 70 and 80 fragments.Photo-desorption of organics is relevant for the detection of such species in the gas-phase of cold environments, where organic synthesis in ice mantles should dominate. We estimate the gas-phase enrichment of some selected species in the light of a protoplanetary disc model around young solartype stars.

We irradiated a (4:1) mixture of water and carbon monoxide with soft X-rays of energies up to 1.2 keV. The experiments were performed using the spherical grating monochromator beamline at National Synchrotron Radiation Research Center in Taiwan. Both monochromatic (300 and 900 eV) and broader energy fluxes (250–1200 eV) were employed. During the irradiation, the H2O + CO mixture was ionized, excited, and fragmented, producing a number of reactive species. The composition of the ice has been monitored throughout both the irradiation and warm-up phases. We identified several products, which can be related through a plausible chemical reaction scheme. Such chemistry is initiated by the injection of energetic photoelectrons that produce multiple ionization events generating a secondary electron cascade. The results have been discussed in light of a model for protoplanetary disks around young solar-type stars.

We irradiated a pure carbon monoxide ice with soft X-rays of energies up to 1.2 keV. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan, exploiting both monochromatic (at 0.3 and 0.55 keV) and broader energy (0.25-1.2 keV) fluxes. The infrared spectra of the irradiated ices showed the formation of a number of products such as polycarbon monoand dioxides C n O m , and chains containing up to 10 carbon atoms. While a gentle increase in the energy absorbed by the ice sample is reflected by an increase in the column densities of newly born species, such correlation breaks down at very high fluxes. In this regime the production yield falls down sharply by about a factor of 100. The refractory residue obtained in the broad energy irradiation is a "compromise" between those obtained with proton irradiation of C 3 O 2 and CO ices in previous experiments. Finally, we discuss the possible implications for space chemistry

We study the photo-desorption occurring in H 2 O:CO:NH 3 ice mixtures irradiated with monochromatic (550 and 900 eV) and broad band (250-1250 eV) soft X-rays generated at the National Synchrotron Radiation Research Center (Hsinchu, Taiwan). We detect many masses photo-desorbing, from atomic hydrogen (m/z = 1) to complex species with m/z = 69 (e.g., C 3 H 3 NO, C 4 H 5 O, C 4 H 7 N), supporting the enrichment of the gas phase.At low number of absorbed photons, substrate-mediated exciton-promoted desorption dominates the photo-desorption yield inducing the release of weakly bound (to the surface of the ice) species; as the number of weakly bound species declines, the photo-desorption yield decrease about one order of magnitude, until porosity effects, reducing the surface/volume ratio, produce a further drop of the yield.We derive an upper limit to the CO photo-desorption yield, that in our experiments varies from 1.4 to 0.007 molecule photon −1 in the range ∼ 10 15 − 10 20 absorbed photons cm −2 . We apply these findings to a protoplanetary disk model irradiated by a central T Tauri star.

Pure CO ice has been irradiated with electrons of energy in the range 150 − 1000 eV with the Interstellar Energetic-Process System (IEPS). The main products of irradiation are carbon chains C n (n = 3, 5, 6, 8, 9, 10, 11, 12), suboxides, C n O (n = 2, 3, 4, 5, 6, 7), and C n O 2 (n = 1, 3, 4, 5, 7) species. CO 2 is by far the most abundant reaction product in all the experiments. The destruction cross-section of CO peaks at about 250 eV, decreases with the energy of the electrons and is more than one order of magnitude higher than for gas-phase CO ionization. The production cross-section of carbon dioxide has been also derived and is characterized by the competition between chemistry and desorption.Desorption of CO and of new species during the radiolysis follows the electron distribution in the ice. Low energy electrons having short penetration depths induce significant desorption. Finally, as the ice thickness approaches the electron penetration depth the abundance of the products starts to saturate. Implications on the atmospheric photochemistry of cold planets hosting surface CO ices are also discussed.