Analytical Potential Energy Functions And Spectroscopic Properties For Electronic States Of BeX (X=Cl,O,S) Molecule

Molecular potential energy function (PEF) is one of the important research directions in atomic and molecular physics. Trough the theoretical calculations to determine the potential energy function expecially for the electronic states of diatomic molecule have been always an important research topic. It can determine molecular energy, force constants, equilibrium geometry and spectroscopic parameters. On the other hand,the potential energy function of diatomic molecule is the key to study the atomic and molecular collision and molecular reaction dynamics.The specific research work as follows. For the first part, we describe the progress for the molecular potential energy function and related theory for analysis the molecular structure and PEF;the second part, we instruct some quantum mechanical calculation methods for researching PEF. These two parts can make ready for the third parts. In the third part, potential energy curves (PECs) for the ground state and several low-lying electronic excited states of BeCl, BeO and BeS molecule have been calculated using the multi-reference configuration interaction (MRCI) method with different basis sets where the Davidson correction was considered as approximation to full CI. Using the group theory and other principles of atomic and molecular reaction statics to determine the symmetries and reasonable dissociation limits for electronic states. The PECs of ground state and electronic excited state for every molecule were fitted to the Murrell-Sorbie(MS) potential function, then use the fitting parameters to calculate the quardratic, cubic and quartic force constants, and further we can determine some spectroscopic datas as harmonic vibrational frequencyωe, the inharmonic vibrational factorωeχe,the rigid-rotational factor Be and the nonrigid-rotational factor ae for each electronic state. In addition, we use Level program to calculate the radial Schrodinger equation of nuclear motion to obtain the vibrational levels for the electronic states.For the ground state and the first electronic state of BeCl molecule, the two states are both doublet, so we calculate several potential energy curves as the same multiplicity as the ground state with basis set aug-cc-pVTZ.Then we determine the dissociation limits and fitting to the Murrell-Sorbie function. For BeO and BeS molecule, we also use MRCI method with basis set aug-cc-pVTZ. Taking the same method as BeCl molecule, we calculate the PECs for several states of the same multiplicity as the ground state for BeO and BeS molecule, then use parameters to obtain the important spectroscopic constants and vibrational levels. We compared results of the three molecule with the present experimental values,for some datas which have no experimental values of BeCl, BeO and BeS molecule, values in our work will provide information for the following research on experimental and theorical respects.