Theoretical Study Of The Nature Of Several Important Small Interstellar Molecules

In this study, the of modern quantum chemistry theory method has been used toinvestigate the structures and performances of NC3O and C4H2+species, at the sametime, the NCO+CH3reaction mechanism has been studied. The results have been listas follows:(1) GAUSSIAN98program is used in the NC3O potential energy surfaceanalysis. At the CCSD(T)//B3LYP level, five stable isomers were obtained such asNCCCO, CNCCO, CCNCO, NCOCC, and [CC(O)NC]. In addition, chainlikeisomers, three-membered-ring isomers, four-membered-ring isomers,five-membered-ring isomers and branched-chain isomers were found also. At theQCISD(T)/6-311G(2d) level, only NCCCO, CNCCO, CCNCO, NCOCC and[CC(O)NC] could be founded in interstellar space or in the laboratory.(2) GAUSSIAN03and NBO5.0programs are used in the C4H2+isomersanalysis. The C4H2+isomers have been studied using the B3LYP/6-311G(d,p) andG3B3methods. Among the ten isomers, there are four chain-like isomers, twothree-membered-ring isomers, and four four-membered-ring isomers. According tothe analysis, HCCCCH is the isomer which has both higher kinetics andthermodynamics stabilities. It may be detected in both the laboratory and Titan'satmosphere. The theoretical results shown in this paper may be help for the futureC4H2+identification in the laboratory or in the Titan atmosphere, and the formationmechanism of benzene. (3) At the B3LYP/6-311G(d,p) and G3B3levels, the singlet and triplet PESs ofNCO+CH3reaction have been investigate. The possible reaction products andreaction mechanism have been discussed, and the result shows that NCO+CH3isapt to reactate along a single potential energy surface. The theoretical calculationsresults are consistent with the experimental reports.