The reaction of excited atomic nitrogen, N(D-2), with the simplest alkene, C2H4, has been investigated under single-collision conditions in crossed beam experiments with mass spectrometric detection. The experimental results clearly show that the N/H exchange channel leading to compounds of gross formula C2H3N is the main reaction pathway and that the reaction proceeds through the formation of a bound intermediate. The title reaction may well be regarded as a good candidate to account for the formation of acetonitrile, CH3CN, in extraterrestrial environments such as the dense atmosphere of Saturn's moon Titan where the ultimate fate of product isomers other than acetonitrile itself, that is 2H-azirine, H2C(N)CH, and ketene imine, CH2=C=NH, is expected to be tautomerization to the most stable structure of acetonitrile.