Theoretical study on structures and stability of PC2S isomers

The structures, energetics, spectroscopies, and stabilities of the doublet PC2S radical are explored at density functional theory and ab initio levels. Seven minimum isomers are located connected by 20 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest-lying isomer is a linear form PCCS 1 whose structure mainly resonates between |
- P=C=C=S−− and |P≡C−C
- =S−− with the former bearing somewhat more weight. The species 1 is predicted to possess great kinetic stability about 50 kcal/mol. Additionally, two high-lying isomers, i.e. bent CCPS 2 (52.0) and bent CCPS 2′ (54.9), are also stabilized by the considerable barriers of 21.0 and 18.1 kcal/mol, respectively. Interestingly, the isomers 2 and 2′ can be easily converted to each other, both of them could coexist. All the three isomers should be experimentally or astrophysically observable. The bonding natures of the isomers 1, 2, and 2′ are analyzed. Their molecular properties including adiabatic ionization potentials and adiabatic electronic affinities are determined at the higher levels G3//B3LYP and G3(MP2)//B3LYP. The calculated results are compared with those of the analogues NC2S and NC2O. Possible formation strategies of the isomers 1, 2, and 2′ in laboratory and in space are also discussed. The present PC2S work represents the first detailed potential energy survey of the PCnS (n>1) series and can provide useful information for future laboratory and interstellar identification of various PC2S isomers.