A Photoionization Reflectron Time-of-Flight Investigation of Phosphorus Chemistry in Extraterrestrial Ices

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2018-05

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University of Hawaii at Manoa

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Multiple phosphorus-containing compounds have been detected in the Solar System (planetary atmospheres, comets, meteorites) along with interstellar and circumstellar environments. Of particular astrobiological interest are alkyl phosphonic acids (RH2PO3, R = methyl, ethyl, propyl, and butyl) extracted from the Murchison meteorite. These phosphonic acids are the only extraterrestrial phosphorus-containing organic compounds thus far discovered and offer a bioavailable and highly soluble form of phosphorus due to its reduced oxidation state. The research of this dissertation investigates the synthesis of phosphorus-containing products of electron-irradiated interstellar ice analogues containing phosphine (PH3), water (H2O), carbon dioxide (CO2), and hydrocarbons such as methane (CH4). Phosphine is known to exist in circumstellar envelopes (IRC +10216), is hypothesized to exist in comets (67P/Churyumov-Gerasimenko), and may serve as the phosphorus source of complex organic compounds such as the alkyl phosphonic acids. Utilizing in situ analysis techniques such as quadrupole mass spectrometry (QMS), tunable-photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS), and infrared spectroscopy (FTIR) in addition to ex situ analysis by secondary-ion mass spectrometry (SIMS) and two-dimensional gas chromatography mass spectrometry (GC×GC-TOF-MS), the intermediates and products of these irradiated ice analogues are characterized to demonstrate the potential to synthesize organic phosphine-containing molecules in astrophysical environments. Notable results include phosphanes (PxHx+2), methylphosphanes (CH3PxHx+1), and phosphorus oxoacids (H3POx, x=1−4, and pyrophosphoric acid (H4P2O7)) along with their alkylated equivalents such as prebiotically significant methylphosphonic acid (CH3P(O)(OH)2) and methylphosphate (CH3OP(O)(OH)2).

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