Complex organics in laboratory simulations of interstellar/cometary ices

Abstract

We present the photochemical and thermal evolution of both non-polar and polar ices representative of interstellar and pre-cometary grains. Ultraviolet photolysis of the non-polar ices comprised of O 2, N 2, and CO produces CO 2, N 2O, O 3, CO 3, HCO, H 2CO, and possibly NO and NO 2. When polar ice analogs (comprised of H 2O, CH 3OH, CO, and NH 3) are exposed to UV radiation, simple molecules are formed including: H 2, H 2CO, CO 2, CO, CH 4, and HCO· (the formyl radical). Warming produces moderately complex species such as CH 3CH 2OH (ethanol), HC(O)NH 2 (formamide), CH 3C(O)NH 2 (acetamide), R-CN and/or R-NC (nitriles and/or isonitriles). Several of these are already known to be in the interstellar medium, and their presence indicates the importance of grain processing. Infrared spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry demonstrate that after warming to room temperature what remains is an organic residue composed primarily of hexamethylenetetramine (HMT, C 6H 12N 4) and other complex organics including the amides above and polyoxymethylene (POM) and its derivatives. The formation of these organic species from simple starting mixtures under conditions germane to astrochemistry may have important implications for the organic chemistry of interstellar ice grains, comets and the origins of life.