The Investigations On The Spectroscopic Parameters And Molcular Constants For SiH And NSe Molecules

The molecular potential energy function is one of the effective ways in the electronic structure andspectral properties of molecules, in the whole space which could give whole space description between theatom and s description of the interaction, at the same time the basis of atomic and molecular collision andreaction kinetics, molecular potential energy curve and its analytical form is one of the important researchdirections in atomic and molecular physics.The auther selects SiH and NSe two diatomic molecules as the research object in this paper, it usingthe convergence of multi reference configuration interaction method (MRCI) and considering the Davidsonmodified and combining with the correlation consistent basis of Dunning as a research tool, at the sametime considering the various correction (the core valance correlation correction, relativistic correction andenergy base extrapolation of this group). And we put the low excited states of SiH(X2Π, A2Δ, B2Σ-, C2Σ+,D2Σ+, F2Π and a4Σ-) and NSe (X2Π,14Π,16Π,12Σ+,14Σ+,16Σ+,14Σ-,24Π and14Δ) two diatomic moleculesinto quantum chemistry MOLPRO program for the high precision of ab initio calculations, and thepotential energy curve of Λ-S states are obtained,and on the basis of the calculations, the potention energycurve of states are obtained by the spin-orbital coupling effect. It fitted the potential energy curves of theelectronic states contains well using MOLCAS program, at the same time, we received spectroscopicconstants of using describe the molecular structure characteristics. Compare these spectroscopic constantswith previously reported experimental values and theoretical value, we find that the spectrum constant ofthis article fit well with experimental data. For each of a diatomic molecule, it is more accurate in theMRCI+Q/CV+DK+56theoretical method.This structured of this paper is following: the chapter one introduces the significance and backgroundof the research work of diatomic molecules; the chapter two gives the theoretical method of calculatingdiatomic molecules (Hartree-Fock, CASSSCF, MRCI theory, energy basis set extrapolation); the chapterthere presents the spectroscopic constants and dissociation limit of nine Λ-S state and twenty-eight statesof NSe molecules, and the spectroscopic constants and dissociation limit of eight Λ-S state and eleven state of SiH molecules and discussed in detail; the chapter four is a summary and outlook.