The lowest doublet potential energy surface for the N(D-2) + C2H4 reaction has been characterized using ab initio molecular orbital theory. The CASSCF/cc-pVDZ calculations predict that the dominant mechanism is the addition of N(D-2) to the CC pi-bond of C2H4 to form a cyclic three-membered intermediate radical rather than the insertion into the CH bond in C2H4. Reaction pathways have also been discussed on the basis of the PMP4(full,SDTQ)/cc-pVTZ//MP2/cc-pVDZ level calculations. The reaction is shown to have several possible products via somewhat complicated reaction mechanisms. The results of RRKM calculations predict that the main product channel is cyclic-CH(N)CH2 (azirine) + H under collision-free conditions.