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Molecular Orbital Study of Neutral-Neutral Reactions concerning HC3N Formation in Interstellar Space

The ab initio molecular orbital method is applied to explore the possibility that neutral-neutral reactions lead to the formation of cyanoacetylene HC3N and its isomers HCCNC and HNCCC in interstellar space. Potential energy surfaces for the formation of the HC3N molecule are examined theoretically for the reactions of the CN radical with acetylene and the C2H radical with HCN and HNC. The calculated result shows that it is possible for HCCCN to be formed from C2H2 + CN and C2H + HNC, because these reactions are exothermic and have no energy barrier. It is not possible for the isomers of the HCCCN molecule to be formed by the neutral-neutral reactions studied here. The different reactivities are discussed by using frontier orbital theory.