AB Initio Theoretical Study On The Spectroscopic Properties Of Antimony-containing Diatomic Halide Molecules

Antimony-containing diatomic halide molecules Sb X(X=F,Cl,Br,I,At)that are formed by the interaction between the heavy metal antimony(Sb)atom and halogen atoms are expected to be used as working media for gas phase chemical energy storage and chemical laser systems because they possess the same valence electron structure with the O₂ molecule.The antimony halide Sb X molecule is also an important intermediate product in the process of etching In Sb semiconductor by halogen X₂ molecule.Grasping the energy and spectral data of electronic states for Sb X is helpful to develop energy storage applications and new chemical laser systems,as well as to explore the reaction mechanism of the etching process.Therefore,it is of great scientific significance and value to study the spectroscopic and transition properties of excited states for Sb X molecules.In addition,the influence of the strong relativistic effect of Sb X molecules on the structure of electronic states and the change rule of spectroscopic properties with the increasing atomic number Z of halogen atoms are the important contents in atomic and molecular physics.In this thesis,we systematically studied the spectroscopic and transition properties of electronic states for the Sb X molecules by using the spin-orbit coupling included ab initio multi-reference configuration interaction(MRCI)method.The details are as follows:(1)The energies and wavefunction of 34?-S states of Sb X molecules have been calculated via the MRCI+Q calculations combined with high-quality correlation-consistent basis sets for the first time.These electronic states are associated with three dissociation channels Sb(~4S,~2D,~2P)+X(~2P)of Sb X molecules,respectively.The Davidson(+Q)correction is used to treat the lack of size consistency of the MRCI method.Based on calculated potential energy curves,the spectroscopic constants of bound?-S states are obtained by solving the Schr(?)dinger equation of nuclear motion.For the calculated spectroscopic data,except for the adiabatic excitation energy(T_e),the other spectroscopic constants are all very close to the experimental values.(2)Based on MRCI+Q calculations,the spin-orbit coupling effect of Sb X is introduced for use with the state interaction method.The properties of predissociation for the excited states a~1? and b~1?⁺are analyzed with the aid of the calculated spin-orbit matrix elements.Under the influence of the spin-orbit coupling effect,the original 34?-S states of Sb X split into 74? states,and the three?-S dissociation channels split into ten?dissociation channels.The ground X~3?^-state of Sb X splits into two?states X₁0⁺and X₂1,The energy splitting?E of Sb F,Sb Cl,Sb Br,Sb I,Sb At are calculated to be 753 cm^-1,808 cm^-1,868 cm^-1,980 cm^-1,1084 cm^-1,respectively.After considering the spin-orbit coupling effect,the calculated adiabatic excitation energies T_e of the first and second excited states a~1?and b~1?⁺are in excellent agreement with the experimental values.From the view of the molecular electronic structure,the fundamental reason for the change of the dissociation relationship of a~1?and b~1?⁺caused by the spin-orbit coupling effect is clarified by analyzing the components of?-state wavefunction.After comparing the energy levels of?-state dissociation channels,it is confirmed that the different Sb X molecules exhibit quite different dissociative behaviors.(3)The transition properties from excited state to ground state are predicted for the Sb X molecules.Based on the MRCI wavefunction and energies of electronic state,the transition dipole moment,Franck-Condon factor,and radiative lifetimes of the selected transitions are calculated.The obtained radiative lifetimes are in good agreement with the previous experimental and theoretical values.With the help of the analysis for the wave function of the ?state,the essence of the spin-orbit coupling effect induced dipole forbidden transition is clarified.(4)The spectroscopic data of Sb X molecule are summarized and calculated,and the variation regularity of spectroscopic and transition properties of Sb X molecules along with the halogen atoms is deduced.The results show that the energy,spectroscopic constant and electric dipole moment of the electronic state of the Sb X molecules change regularly with an increasing atomic number Z.However,the change of the radiative lifetimes for a~1?and b~1?⁺states does not show a certain rule.With the aid of electric dipole moments of the?-S states and?-S compositions of the?wavefunction,we analyze the reason for this situation and a reasonable explanation is provided.