Sublimation of Laboratory Ices Millimeter/Submillimeter Experiment (SubLIME): Structure-Specific Identifications of Products from UV-photolyzed Methanol Ice

Submillimeter/far-IR spectroscopy was used to detect and quantify organic molecules sublimated after the ultraviolet photolysis (at 12 K) and warm-up (up to 300 K) of a methanol (CH3OH) ice sample. Eleven sublimated photoproducts were uniquely identified: carbon monoxide (CO), formaldehyde (H2CO), ketene (C2H2O), acetaldehyde (CH3CHO), ethylene oxide (CH2OCH2), vinyl alcohol (CH2CHOH), ethanol (CH3CH2OH), dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), glycolaldehyde (HOCH2CHO), and acetone ((CH3)2CO). Two additional products were detected in the photolyzed ice by Fourier-transform infrared (FTIR) spectroscopy: carbon dioxide (CO2) and methane (CH4). The rotational temperatures and gas densities were calculated for the organics containing two or more C atoms via a rotation diagram analysis, and the gas-phase submillimeter/far-IR technique was used in tandem with mass spectrometry and FTIR spectroscopy of the ice during photolysis. The abundance ratios of the sublimated species (normalized to methanol) were compared to those observed in hot cores (Orion-KL, Sagittarius B2(N), and IRAS 16293-2422(B)) and in comets C/2014 Q2 (Lovejoy) and 67P/Churyumov–Gerasimenko.