  The origin of the atmosphere of the largest moon of Saturn, Titan, is poorly
understood and its chemistry is rather complicated. Ground-based
millimeter/sub-millimeter heterodyne spectroscopy resolves line shapes
sufficiently to determine information in Titan's atmospheric composition (on
vertical profiles and isotopic ratios). We test the capabilities of the Swedish
Heterodyne Facility Instrument (SHFI), Receiver APEX-1, together with the
Atacama Pathfinder EXperiment APEX 12-m telescope for Titan's atmospheric
observations. In particular we present sub-millimeter observations of the
CO(2-1) and HCN(3-2) lines of the Titan stratosphere with APEX, and with SHFI
taken during the Science Verification (SV) instrument phase on March and June
2008. With the help of appropriate radiative transfer calculations we
investigate the possibility to constrain the chemical concentrations and
optimize the performance of the APEX-1 instrument for inferring vertical
profiles of molecular components of the atmosphere of Titan.
