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Project Progress

David Summers & Bishun Khare- Work this year focused on the reduction of NO to ammonia by FeS minerals in aqueous solution. This represents a third nitrogen fixation pathway in addition to the ones identified in previous work. Product yields of ~50% for ammonia were measured. The yield of ammonia formation appears to peak at pH 7 and falls of into acidic or basic conditions. Currently, we are using isotope labeling to identify a gaseous product observed with peaks at 2235, 2100, 1300, and 1270 cm^-1 in the IR. We have conducted isotope labeling experiments with ²D₂O, H₂¹⁸O, and N¹⁸O. The gaseous compound(s) appear to be CNO, (NCO)₂, or some related species (a cyanato or isocyanato species). HCNO, HNCO, HOCN, and HONC have been ruled out. The gaseous product is formed in yields that are unaffected by the pH, but which increase as the amount of FeS is increased. We are currently conducting ¹³C isotope labeling experiments and looking to the ¹⁴N isotope fractions of all the reactions we have been studying. These results were presented in an invited paper at the 2008 COSPAR (Committee on Space Research) and at the 2008 Astrobiology Science Conference.