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Theme 4

Solid ice photo-processing pathways to complex organic molecule formation

WP4-1 Photo-processing of realistic interstellar ice analogues.

During early stages of star formation en route from dense clouds to the proto-planetary phase, the interstellar material from the nascent cloud may be subjected to intense irradiation with energetic photons. Novel experimental setups and techniques (CRYOPAD2 and MATRI2CES at UL and a new end-station to be constructed at the ASTRID2 Synchrotron source at AU) allow us to measure the formation of increasingly complex molecules upon VUV-processing of realistic ice mixtures in situ, i.e., without air exposure and thermal heating as commonly used in ex situ studies. Ice mixtures will contain dominant components as identified by the Spitzer Space Telescope: H2O, CO, CO2, CH3OH, NH3, and CH4, but also trace species as identified via infrared observations or identified as reaction products under Theme 2 and 3. Photo-desorption and photo-dissociation rates as well as reaction networks and rates for photo-catalytic reactions will be measured. Experimental measurements will be complemented by theoretical simulations of the relaxation mechanisms of the neutral molecular fragments resulting from the UV absorption, as previously done by BH for ethanol photolysis. This will facilitate the identification of reaction pathways and enable the characterization of catalytically active pockets within the icy matrix. Results will be compared to ALMA observations of hot cores, where the ices are sublimated and the resulting gas phase species are measured with high accuracy and sensitivity in the gas7, and to JWST observations. Conversely, observed complex organic molecules that were not predicted will stimulate new experiments and models.

Initial key reaction: Glycine formation

WP4-2 Photo-catalytic activity of ice-embedded nanoparticles.

We will investigate the photo-catalytic effect of nano-particles (PAHs, Theme 1 dust grain analogues) embedded in mixed ices, as catalytic cores that may enhance the formation of complex organic molecules via catalytically active sites, plasmonic field enhancement or charge effects. Guided by the findings under theme 2 and 3 we will investigate whether photo-processing of ice embedded PAHs and functionalized PAHs provide a pathway to formation of cytosine. The wavelength and polarization dependence of the photo-catalytic processes will be studied. Experimental measurements will be complemented by theory and observations.