Theoretical Study Of Spectroscopic Constants And Transition Properties Of SiH And SiH~+

Molecular potential energy function(PEF)describes molecular internal energy,geometric structure,and spectroscopic constants,which are the important in the atomic and molecular physics.In addition,Molecular potential energy function has important influence on laser cooling.Ultracold molecules can be used in many fields of research.But direct laser cooling of molecules is a challenge because of their complex molecular structure.Since the direct cooling of SrF molecule was successfully reported in 2010,more and more molecules have been performed experimentally.However the criteria of candidates for laser cooling must follow these keys:(i)highly diagonal Franck-Condon factors(FCFs),(?)shortly radiative lifetimes ? for rapid laser cooling,(iii)if intervening electronic states exist,it is necessary to ensure that they have no effect on the laser cooling cycle.This paper will study spectroscopic constants and transitions properties of SiH and SiH+.If the molecules are suitable for laser cooling,schemes to laser cooling molecule are designed.The main contents of this paper are as follows:In this paper,potential energy curves(PECs)of electronic states for SiH and SiH+ are calculated based on multi-reference configuration interaction.In order to obtain more accurate results,Davidson corrections,core-valence correlation,scalar relativistic effects,and spin orbit coupling(SOC)effects are considered.By solving the radical Schrodinger equation,the spectroscopic constants of these states are obtained.In addition,the transitions properties of SiH and SiH+,including PDMs,TDMs,FCFs and radiative lifetimes,are calculated to determine the suitability for laser cooling.Firstly,the potential energy curves and spectroscopic constants of SiH are studied,which agree well with the experimental results.In addition,the SOC effects have little influence on spectroscopic constants.The transitions X2??A2? and X2??C2?+have highly diagonally distributed FCFs and shortly radiative lifetimes.Besides,the intervening electronic states have no effect on the laser cooling cycle,which meet the requirement of laser cooling.This is to say,X2??A2?and X2??C2?+ are suitable for laser cooling of the SiH molecule.Schemes to laser cooling SiH molecule are designed,and the proposed laser cooling drives for the transitions X2?(V")?A2?(V')and X2?(V")?A2?+(V')both use three wavelengths.Furthermore,It is the first time that the transitions properties of X2??C2?+are researched.Then,the potential energy curves for the seven ?-S states(X1?+,a3?,A1?,b3?+,C3?-,d3?.and B1?)and fifteen Q states(X1?0++,a3?O-,0+1,2,A1?1,b3?0-,1+,c3?O+,1-,d3?0-,0+,1,2,and B1?2)of SiH+ cation are computed.The spin-orbit coupling has great effect on B1?,b3?+,c3?-,and d3?.The spin-orbit coupling leads to avoided crossing between B1?2 and d3?2 states,c3?1-and b3?1+ states,respectively.And the B1?2 state has a double-well potential resulting from the avoided crossing.In addition,the transitions properties for the transitions X1??A1?,A1??B1?,a3??d3?,a3??c3?-,c3?-?d3?,X1?0++?a3?0+,and X1?0++?a3?1 of SiH+ are calculated.It is indicated that the states a3?0+,and a3?1 are prohibitive to the cooling cycle.Meanwhile,It is the first time that the spin-orbit coupling calculation is carried out on SiH+.