The nitrosyl isocyanate (ONNCO) has been generated from a heterogeneous reaction of gaseous nitrosyl chloride with silver isocyanate and studied for the first time in the gas phase. This structurally and energetically novel transient specimen is characterized by Hel photoelectron spectroscopy combined with DFT calculations. Both the calculations and the spectroscopic results suggest that the molecule adopts an open-chain trans structure. The observed decomposition products indicate the formation of ONNCO and further confirm the previously reported decomposition pathway.