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A theoretical study of the molecular structure of uraniumdicarbidehas been carried out employing DFT, coupled cluster, and multiconfigurationalmethods. A triangular species, corresponding to a 5A2electronic state, has been found to be the most stable UC2species. A triplet linear CUC species, which has been observedin recent infrared spectroscopy experiments, lies much higher in energy.A topological analysis of the electronic density has also been carriedout. The triangular species is shown to be in fact a T-shape structurewith a U–C interaction which can be considered to be a closed-shellinteraction. [ABSTRACT FROM AUTHOR]

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]