Ab Initio Study Of Spectroscopic Constant And Anharmonic Force Field Of SiH_nR_m(n=0,2, M=2;R=F,Cl)

The study of SiH_nR_m（n=0,2,m=2;R=F,Cl） can be traced back to 1598, because it is hoped that the semiconductor material has made breakthrough progress, a series of further research in chemical and physical for compounds which containing Si. Theoretical study of these molecules can provide the reference for experimental study.The main work of this paper is to study the equilibrium spectroscopic constants and the anharmonic force field of SiF₂, SiH₂F₂ and SiH₂Cl₂ by high level ab initio calculations.Firstly, we calculate the equilibrium geometry structure of SiF₂ using B3 LYP, B3PW91, MP2 with cc-pVTZ and cc-pVQZ; on the base of getting the equilibrium geometry, we calculate the spectroscopic constants and anharmonic force field of SiF₂. In addition, we compared some spectroscopic constants, like the equilibrium geometry structures, harmonic and fundamental frequencies, coriolis coupled constants and so on, with the relevant experimental and theoretical data. Besides, we predicted the other constants, such as the third-order and forth-order force constants. The results show that the MP2 results are in excellent agreement with experiment.Secondly, we calculated the equilibrium geometry structure and the anharmonic force field by the same level of theory for SiH₂F₂ and SiH₂Cl₂. From the calculated results, we can see that the calculated values of MP2 method are perfectly agreement with the experimental data. Besides, predictions of some spectroscopic constants are expected to be useful for the future experimental work.The results also show that with the same method, results using the basis set of cc-pVQZ are closer to the experimental data than the results using the basis set of cc-pVTZ.