Theoretical study of the spectra and radiative transition properties of 6Li32S

Abstract

Low-lying electronic states (X2, A2+, a4, B2, b4, C2, F2-, E2+ and D2) of the 6Li32S molecule are computed at the aug-cc-pV5Z/MRCI level. The potential energy curves are presented for these states; the corresponding spectroscopic constants are reported. Electronic transition moment, Einstein coefficients, Frank-Condon factors and radiative lifetimes for the A2+-X2, B2 -X2, C2 -X2 systems are calculated. The balanced distance between two nuclei, harmonic frequencies and inertia moment of ground state X2 are predicted in this paper, and they are in accordance with their corresponding experimental data. The balance distances between the two nuclei in the electronic states of b4, C2, D2 are all longer than 4 , so they are very unstable. The D2 electronic state will dissociate to Li+ ion and S- ion: they are far from each other. The electronic transition dipole moment, Einstein coefficient, Franck-Condon factor and radiative lifetime in transition from lowest excited A2+ state to ground state X2 are predicted in this paper. The electronic transition dipole moments from three low lying electronic state A2+, B2 and C2 to the ground state X2 are calculated at the aug-cc-pV5 Z/MRCI level. The results show that the electronic transition dipole moment of A2+X2 has a small positive value while the nucleus distance is short, and rapidly decreases down to a small negative value with the nucleus distance increasing to around balance distance. Then it is stable about zero value while the nucleus distance continually increases. The electronic transition dipole moment of B2 X2 has a small negative value (which is larger than that of A2+ X2) at a short nucleus distance, and rapid increases up to a small positive value with the nucleus distance increasing to about balance distance. Then it slows down to zero while the nucleus distance increases to about 4. Finally it turns stable about zero value while the nuclei distance continually increases. The electronic transition dipole moment of C2 X2 is more sophisticated, but it has a large value than other two transitions. So the low-lying electronic state A2+ is stabler than B2, and B2 is stabler than C2 . The results also show that the ground state X2 and the lowest excited state A2+ have similar IR frequencies, their difference is within 8 cm-1, so they cannot be distinguished by IR spectrum. The A2+ has a balanced distance about 0.076 shorter than ground X2, which implies that A2+ has stronger chemical bond than ground X2 .