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The Cassini mission performed 127 targeted flybys of Titan during its 13-yearmission to Saturn, culminating in the Grand Finale between April-September2017. Here we demonstrate the use of the Atacama Large Millimeter/submillimeterArray (ALMA) to continue Cassini's legacy for chemical and climatologicalstudies of Titan's atmosphere. Whole-hemisphere, interferometric spectral mapsof HCN, HNC, HC3N, CH3CN, C2H3CN, C2H5CN and C3H8 were obtained using ALMA inMay 2017 at moderate (~0.2'', or 1300 km) spatial resolution, revealing theeffects of seasonally-variable chemistry and dynamics on the distribution ofeach species. The ALMA sub-mm observations of HCN and HC3N are consistent withCassini infrared data on these species, obtained in the same month.Chemical/dynamical lifetimes of a few years are inferred for C2H3CN and C2H5CN,in reasonably close agreement with the latest chemical models incorporatingsticking of C2H5CN to stratospheric aerosol particles. ALMA radial limb fluxprofiles provide column density information as a function of altitude,revealing maximum abundances in the thermosphere (above 600 km) for HCN, HNC,HC3N and C2H5CN. This constitutes the first detailed measurement of the spatialdistribution of HNC, which is found to be confined predominantly to altitudesabove 730 $\pm$ 60 km. The HNC emission map shows an east-west hemisphericasymmetry of (13$\pm$3)%. These results are consistent with very rapidproduction (and loss) of HNC in Titan's uppermost atmosphere, making thismolecule an effective probe of short-timescale (diurnal) ionospheric processes.

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale