Formation of Insoluble Organic Material from the Ultraviolet Irradiation of Laboratory Ice Photolysis Residues

We present preliminary results from the study of ice photolysis residues which were exposed to ultraviolet (UV)/extreme UV (EUV) photon radiation. The residues were produced from the simultaneous deposition and UV irradiation of ice mixtures of astrophysical interest (H2O, CH3OH, CO, NH3, without/with N2 and/or O2, and without/with small quantities of aromatic compounds) at 15–20 K using an H2 lamp, which emits 10.2-eV (121.6 nm) Lyman-α photons and a continuum at 7.5–8 eV (155–165 nm). After warm-up to room temperature and subsequent sublimation of volatile compounds, the refractory materials (residues) recovered at room temperature were analyzed with infrared (IR) microscopy and then further irradiated with UV/EUV photons at a synchrotron facility, on a beamline providing a broad-band photon beam in the 4–45-eV range with a ~1016 photons s-1 flux.2 The residues were UV/EUV irradiated with increasing photon doses ranging from ~1018 to ~1021 photons, i.e., covering 4 orders of magnitude and relevant to those experienced by ice-coated grains in the protosolar nebula.1. After UV/EUV irradiation, residues were analyzed with IR microscopy and the data compared to those before irradiation to identify changes in chemical composition as a function of the photon dose. UV/EUV-irradiated residues were also analyzed with other techniques such as nanoscale secondary-ion mass spectrometry (nanoSIMS) to the study the changes in isotopic composition, and scanning transmission electron microscopy to look at variations in structure and C bonding distribution. Results will be compared with data from extraterrestrial materials, in particular, meteoritic insoluble organic material (IOM) and interplanetary dust particles (IDPs).