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We report an ab initio study of the quintet states of molecular oxygen. The calculations are carried out employing the multireference single and double excitation configuration interaction package. Potential energy curves of the six quintet valence states dissociating into ground state atoms and of the four quintet states dissociating to ion-pair atoms were computed. A number of bound quintet Rydberg series converging to the a4Πu and b4Σ-g states of the O2+ cation have been identified. [ABSTRACT FROM AUTHOR]

In this contribution we first report new ab initio self-consistent field configuration interaction calculations of the first excited adiabatic potential of 1Σ+ symmetry, the 21Σ+ or B1Σ+ state, which presents two minima and can thus be seen as made up of the Rydberg E1Σ+ and the valence V1Σ+ states. Based on the computed 21Σ+ potential, we devised a theoretical procedure to compute the vibronic structure in order to try to explain the energy levels observed in the region above 76 254.4 cm-1 which display an irregular vibrational structure, indicative of spectral perturbations. We try to find out which representation of the electronic states, the diabatic or the adiabatic one, is best suited to replicate the lowest observed vibronic levels of the E and V states. To this end, we deduce, from the 21Σ+ potential and its complementary adiabatic potential, two diabatic potentials. We then carry out a coupled equation treatment based on these diabatic potentials. The results of this treatment indicate that, in the present case, the adiabatic representation is better than the diabatic one to describe the observed vibronic levels. This is due, as expected, to the existence of a strong electrostatic interaction between the two diabatic potentials. [ABSTRACT FROM AUTHOR]

We report an ab initio study of the low-lying valence and Rydberg states of HBr. The calculations are carried out employing the multireference single- and double-excitation configuration interaction method including the spin–orbit interaction. The first excited adiabatic potential of 1Σ+ symmetry presents two minima which correspond to the Rydberg E1Σ+ and valence V1Σ+ observed states. We calculate the vibrational levels of these two states using a coupled-channel treatment based on the two diabatic potentials deduced from the ab initio adiabatic potentials and the Rydberg–valence interaction. The chaotic energy separations between the observed levels are well reproduced in the calculations. We have also obtained for the first time theoretical data for numerous Rydberg states of HBr lying in the (66–79) × 103 cm−1 excitation energy interval. The calculated spectroscopic parameters are found to be in good agreement with experiment and provide a basis for future studies of radiative and non-radiative processes in the HBr molecule. [ABSTRACT FROM AUTHOR]

We report an ab initio study of the quintet states of molecular oxygen. The calculations are carried out employing the multireference single and double excitation configuration interaction package. Potential energy curves of the six quintet valence states dissociating into ground state atoms and of the four quintet states dissociating to ion-pair atoms were computed. A number of bound quintet Rydberg series converging to the a4Πu and b4Σ-g states of the O2+ cation have been identified. [ABSTRACT FROM AUTHOR]