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Project Progress

In the Cosmic Ice Laboratory we simulate the low-pressure and temperature environment of space using a high-vacuum chamber and a cryostat. Ice samples condensed onto a cooled mirror inside the cryostat are irradiated with 1-MeV protons, to simulate cosmic-ray bombardment, or are photolyzed to simulate vacuum-UV exposure. Motivated by detections of glycolaldehyde (HOCH₂CHO) and ethylene glycol (HOCH₂CH₂OH) in the interstellar medium and, for ethylene glycol, in comet Hale-Bopp, we examined the low-temperature formation of these molecules. We found that irradiated methanol-containing ices produced ethylene glycol, and that ices containing this molecule produce glycolaldehyde, a simple sugar. In addition we determined that energetic processing of aliphatic alcohols produces aliphatic aldehydes and vice versa.

Other new results are the detection of several amino acids in residues that resulted from ice irradiations. We performed many ice irradiation and photolysis experiments on acetonitrile (CH₃CN) since it is a nitrile of interest for comets, Titan, and circumstellar regions. IR spectra of irradiated or photolyzed CH₃CN show the formation of HCN, ketenimine, and CH₃NC, seen in the left-hand figure below. IR spectra of the residue remaining after warming to 290 K show broad features in the 4.4 — 4.7 um (2200-2080) cm^-1) region, consistent with C=N bonded species. However, only through chemical analysis of these residues can the details of their composition be revealed. The right-hand figure below is an HPLC trace of a residue showing many peaks not seen in the blank. Amino acids such as glycine, alanine, aspartate, and glutamate were identified in subsequent chemical analyses completed by Jason Dworkin. The complete set of ice experiments included both unlabeled and (three different) ¹³C-labeled CH₃CN ices, along with controls to test the extraction and HPLC protocols. Details about the instrumentation and protocols that made possible these identifications are given in the discussion of the Astrobiology Laboratory. These experiments lead to our next step, the irradiation of nitriles in water-dominated ices and the search for amino acids.

Outreach

• The summer (‘05) project, “Irradiation of Nitrile-Containing Ices: A Laboratory Study”, was completed by Zachary Pozun, an astrobiology student intern. He took part in setting-up and performing various ice irradiation experiments and measuring infrared spectra of the ices as a function of dose and temperature. He documented isotopic shifts in many products, e.g. OCN-, HCN, CH4, and CH3CNH. The complete set of ice experiments included both unlabeled and (three different) 13C-labeled CH3CN ices. These isotopically-labeled experiments were used to confirm reaction pathways for identified products.
• Two undergraduate astrobiology courses were taught (fall, 2004)

Equipment

• New IR spectrometer brought on line; instrument purchased with separate NASA funding (needed for new work on biomolecules)
• New cryostat installed for experiments at temperatures below 12 K

Web page highlights

• Complete redesign and expansion of the Web site for the Cosmic Ice Laboratory http://www-691.gsfc.nasa.gov/cosmic.ice.lab/

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