text: HCN has been measured in Titans atmosphere by four instruments on the Cassini space probe, one instrument on Voyager, and one instrument on Earth. One of these measurements was in situ, where the Cassini spacecraft dipped between  above Titans surface to collect atmospheric gas for mass spectrometry analysis. HCN initially forms in Titan's atmosphere through the reaction of photochemically produced methane and nitrogen radicals which proceed through the HCN intermediate, e.g., (CH + N → HCN + H → HCN + H). Ultraviolet radiation breaks HCN up into CN + H; however, CN is efficiently recycled back into HCN via the reaction CN + CH → HCN + CH.