Theoretical Investigations On Spectroscopoc Properties Of Loy-lying Electronic States Of Several Diatomic Molecules Or Cation

Potential energy function (PEF) is the complete description of electronic structure for moleculeitself (such as, geometry, force constants and spectrum properties). The potential energy function of thediatomic molecule is considered as the basic issues. Because of, it is only the function of the internucleardistance. Molecular potential energy curve (PEC) is one of the important branches in atomic and molecularphysics. At the same time, it is also the PEF of the core movement, which is the foundation to investigateatomic and molecular collision and reaction and is of special importance in the atom-cluster growth,dissociation and stability analyses.In the present work, the PEF, PEC, spectroscopic parameters and molecular constants for fourdiatomic molecules or cation (CS, CBr+, BeAr+and C+2) are calculated. The effects on the spectroscopicparameters and molecular constants by some corrections are considered. The molecule or ion containingcarbon is fundamental importance, which has been attracting much interest not only in astrophysics but alsoin atmospheric science. For halogenated carbenes, few results can be found about the CBr molecule, inparticular about the CBr+cation. There is considerable interest in studying various physical and chemicalforces which contribute to the stabilities of electronic states of diatomic molecules formed by rare-gaseousand metal atoms or ions. However, it’s difficult to observe directly diatomic molecules containing arare-gaseous atom in experiment. Naturally, the accurate theoretical spectroscopic parameters of suchdiatomic molecules are important to comprehend various physical and chemical forces.First, the PECs of18Λ-S states of CS molecule,12Λ-S states of CBr+cation,3Λ-S states ofBeAr+cation and24Λ-S states of C2+cation are calculated using the internally contracted multi-referenceconfiguration interaction method (icMRCI) with Dunning’s correlation consistent basis sets. The effects onthe spectroscopic parameters and molecular constants by the Davidson, core-valence correlation, scalarrelativistic corrections and the extrapolated of totle energies calculated to limit are considered in the presentwork. We get the spectroscopic parameters (De, Te, Re, ωe, ωexe, ωeye, Beand αe) by solving therovibrational Schr dinger equation with Numerov’s method. For BeAr+cation, the complete vibrationalstates are also obtained by fitting the PECs. For each vibrational state, the vibrational level G(ν), inertialrotation constant Bνand centrifugal distortion constant Dνare calculated when J=0. The results arecompared with the other theoretical and experimental values available, and the comparison shows that excellent agreement exists between the present results and the available experiments.Then, The spin-orbit (SO) coupling effect on the spectroscopic parameters is included usingicMRC with the fall Breit-Pauli operator with all-electron basis set. The PECs of50states of CSmolecule,23states of CBr+cation,4states of BeAr+cation and54states of C2+cation arecalculated. And the spectroscopic parameters for each state are determined. The effects on thespectroscopic parameters by the Davidson, core-valence correlation, scalar relativistic corrections and theextrapolated of totle energies calculated to limit are considered on the basis of the SO coupling effect.Finally, The transition properties of CBr+and BeAr+cation are studied with the help of LEVELProgram. For CBr+cation, we calculate the Frank-Condon factors, transitions dipole moments and radiativelifetimes at different vibrational levels for the two transitions, a3Π10+-XΣ+0+and a3Π1-X1Σ+0+. For BeAr+cation, we calculate the Frank-Condon factors, transitions dipole moments and radiative lifetimes atdifferent vibrational levels for the three transitions, A2Π1/2-X2Σ+1/2, A2Π3/2-X2Σ+1/2and22Σ+1/2-X2Σ+1/2.On the whole, by comparing the present results with the experiments, the Davidson, core-valencecorrelation, scalar relativistic corrections SO coupling effect and the extrapolation obviously improve thespectroscopic parameters quality. The transition properties are studied which should be good references forfuture experimental or theoretical research.