[P-CG26] New Developments of Planetary Sciences with ALMA

[PCG26-08] Effect of GCR on the atmospheric chemistry process of Titan: a new constraint by the determination of 14N/15N in CH₃CN with ALMA

*Takahiro IINO¹, Hideo Sagawa², Takashi Tsukagoshi³ (1.Information Technology Center, the University of Tokyo, 2.Kyoto Sangyo University, 3.National Astronomical Observatory of Japan)

Keywords:Titan, ALMA

By analyzing archival data obtained by the Atacama Large Millimeter/submillimeter Array (ALMA), we have successfully detected rotational transitions of CH₃C¹⁵N (J = 19--18) at the 338 GHz band in Titan's atmospheric spectra.
Using the radiative transfer analysis, comparing those observations with the simultaneously observed CH₃CN (J = 19--18) lines at the 349 GHz band, which probe from 160 to ~400 km altitude, we then derived ¹⁴N/¹⁵N in CH₃CN as 125 (+145/-44). The best-fit value suggests that ¹⁴N/¹⁵N for CH₃CN is higher than values that have been previously observed and theoretically predicted for HCN and HC₃N.
This may be explained by the different N₂ dissociation sources according to the altitudes, as suggested by a recent photochemical model.