Computational Study ofthe Reaction of P숫 Acetylene: Does Spin-Crossing Playa Significant Role?

A computational study of the reaction of P(3P) with acetylene has been carried out. The only exothermicproducts correlating with the reactants are PCCH(2Π) H(2S). Two different pathways leadingto these products that are apparently barrier-free have been found.Both pathways involve isomerization into open-chain intermediatesfollowed by direct elimination of a hydrogen atom. The possibilityof spin-crossing has been considered because the species on the singletsurface are considerably more stable than those on the triplet one.On the singlet surface, there are other possible channels for thereaction, namely, cyclic PC2H(2A′) H(2S) and CCP(1Σ) H2(1Σg). A computationalkinetic study shows that, in agreement with the experimental evidence,the major products are PCCH(2Π) H(2S) at all temperatures. Only at very high temperatures isCCP(1Σ) H2(1Σg) formed in non-negligible amounts.Therefore, only PCCH눚⺕ be formed in the interstellarmedium. [ABSTRACT FROM AUTHOR]