Pure thionyl azide SO(N-3)(2), which is the only gaseous reaction product, has been generated in a vacuum by the heterogeneous reaction of SOCl2 vapor with AgN3 at room temperature at a SOCl2 vapor pressure of 1 x 10(-3) Torr. Evidence for the formation of SO(N-3)(2) is given by on line photoelectron spectroscopy (PES) combined with outer valence Green's function (OVGF) calculations with the 6-311++G(2df) basis set. The good agreement between the PES experiment and the OVGF calculation shows that SO(N-3)(2) has C-1 symmetry. The first ionization energy of SO(N-3)(2) is 10.18 eV.