The chemical mechanism of the 1 PN formation was successfully studied by using the CCSD(T)/6-311++G(3df,3pd) level of theory. The 1 NH 3 + 3 PH and 4 P+NH 3 reaction paths are not energetically favorable to form the 1 PN molecule. However, the 3 NH+ 3 PH, 4 N+ 3 PH 3 , 4 N+ 3 PH, 4 P+ 3 NH, and 4 P+ 2 NH 2 reaction paths to form the 1 PN molecule are only energetically favorable by taking place through specific transition states to form the 1 PN molecule. The NH 3 + 3 PH, 4 N+ 1 PH 3 , NH 3 + 4 P, and 4 N+ 2 PH 2 reactions are spin-forbidden and the probability of hopping for these reactions was estimated to be 0 by the Landau–Zener theory. This is the first detailed study on the chemical mechanism for the 1 PN formation.