ALMA OBSERVATIONS OF HCN AND ITS ISOTOPOLOGUES ON TITAN

作者：Molter Edward M^*; Nixon C A; Cordiner M A; Serigano J; Irwin P G J; Teanby N A; Charnley S B; Lindberg J E

来源：Astronomical Journal, 2016, 152(2): 42.

DOI：10.3847/0004-6256/152/2/42

• planets and satellites: atmospheres
• planets and satellites: individual (Titan)

We present sub-millimeter spectra of HCN isotopologues on Titan, derived from publicly available ALMA flux calibration observations of Titan taken in early 2014. We report the detection of a new HCN isotopologue on Titan, (HCN)-C-13-N-15, and confirm an earlier report of detection of DCN. We model high signal-to-noise observations of HCN, (HCN)-C-13, (HCN)-N-15, DCN, and (HCN)-C-13-N-15 to derive abundances and infer the following isotopic ratios: C-12/C-13 = 89.8 +/- 2.8, N-14/N-15 = 72.3 +/- 2.2, D/H = (2.5 +/- 0.2) x 10(-4), and HCN/(HCN)-C-13-N-15 = 5800 +/- 270 (1 sigma errors). The carbon and nitrogen ratios are consistent with and improve on the precision of previous results, confirming a factor of similar to 2.3 elevation in N-14/N-15 in HCN compared to N-2 and a lack of fractionation in C-12/C-13 from the protosolar value. This is the first published measurement of D/H in a nitrile species on Titan, and we find evidence for a factor of similar to 2 deuterium enrichment in hydrogen cyanide compared to methane. The isotopic ratios we derive may be used as constraints for future models to better understand the fractionation processes occurring in Titan's atmosphere.

• 出版日期2016-8