Theoretical Study On Potential Energy Surface Of The HSCCS Radical

Reactions of small radicals with neutral molecules play a significant role in diverse environments such as combustion flames, the interstellar medium (ISM), and planetary atmospheres such as Saturn' moon Titan. Those researches are important to predict the physics and chemistry of interstellar medium and early evolvement of stars. Sulfur has been detected in interstellar space, so sulfur-containing carbon chains interest the researchers. C₂S and C₃S have been observed astronomically. As a result, quantum chemical investigations on the potential energy surface of HSCCS radical have been carried out in this thesis. This article includes the isomerization of HSCCS radical, the structure and stableness of isomers, the potential energy surface including energy of isomers and transition states. Some conclusions that are made in the present thesis may be helpful for future theoretical and experimental studies. The main results aresummarized as follows:1. The potential energy surface (PES) of HSCCS radical including eight isomers and twelve transition states is obtained at MP2/6-311G(d,f) level. Single point energy is obtained by CCSD(T)/6-311G(d,f) method. The calculated resultsshow that the isomer ml has the lowest energy. The energy of isomer m2 is higher than that of ml by 35.80kJ/mol. The isomers mland m2 are all belong to Cs symmetry. The isomer ml can isomerize into isomer m2 via transition state TS1. The energy of transition state TS1 is higher than that of isomer m2 by 3.9kJ/mol at MP2 level, while it is lower than the energy of isomer m2 by 14.6kJ/mol at CCSD(T) level. So the isomer m2 can easily isomerize into ml. The isomer ml can isomerize into isomer m6 via transition state TS6. The isomer m6 is not a stable isomer for the non-barrier isomerization. The isomers m4 and m5 are unstable isomers for the low barrier. The isomer m3 can transform into m4, m5 and ml via transition states TS3, TS4 and TS2. The isomer m3 is a stable isomer because of the high barriers. The isomer m7 is unstable for the low barrier, about 35kJ/mol, of isomerization between isomers m6 and ml. In certain conditions, we predict that the isomer ml with higher thermodynamical stability should be observed in experiments.2. The isomer m8 is unstable. It will dissociate to the CS and HCS via transition state TS12. The barrier is 45.03kJ/mol. The barrier of isomerization between TS12 and isomer m8 is 37.57kJ/mol when CS and HCS are reactants, while m8 will transform easily into m6 with lower energy via transition state TS10. Because the isomer m6 is unstable for the non-barrier isomerization between m6 and ml, the most feasible pathway can be summarized as follows:R -* TS12 -+ m8 ^TSIO -* m6 -+ TS6 -> ml The product is not the isomer m3 but the isomer ml with higherthermodynamical stability. Although the isomer m3 was detected in experiment, the calculated results show that the isomer m6 should transform into isomer m3 via transition state TS7 when CS+HCS are reactants and the product is the isomer m3. The formation of isomer ml is easyer than m3. It should be research detailedly in future theoretical and experimental studies.