High Spectral Resolution SOFIA/EXES Observations of C2H2 Towards Orion IRc2

Acetylene (C2H2) is one of the primary building blocks in the formation of larger hydrocarbons, ring molecules and PAHs in the interstellar medium (ISM). This is especially true for the formation of complex organic molecules (important for life) in hot molecular cores, which are the warm, dense regions surrounding massive protostars. Because C2H2 has no permanent dipole moment, it can only be observed via transitions in the mid-infrared (MIR). High spectral resolution is required to resolve the individual ro-vibrational transitions. I will present recently accepted SOFIA/EXES observations of C2H2 towards the Orion hot core, which has one of the richest molecular chemistries observed in the ISM associated with massive star formation. In the MIR, the Orion hot core composition is best sampled by the closest, bright background continuum source in this region, IRc2. In addition to high spectral resolution, SOFIA’s smaller beam (compared to previous IR missions such as ISO) can isolate emission from a single infrared source sampling only the material from the foreground Orion hot core. We detect C2H2, 13CCH2 and HCN with high-S/N. Our data show distinct ortho and para C2H2 ladders towards the Orion hot core for the first time, with a C2H2 ortho to para ratio (OPR) of only 1.7 - much lower than the high temperature equilibrium value of 3. In addition, I will also describe our ongoing Orion hot core line survey in the MIR using SOFIA/EXES and IRTF/TEXES and show some new observations taken in the last year.