Study on the spectroscopic parameters and transition probabilities of 25 low-lying states of the AlC+ cation

- Effect of core-valence correlation and scalar relativistic corrections is included.
- PECs are extrapolated to the CBS limit.
- TDMs between two states and FC factors of some transitions are calculated.
- Spectroscopic properties and vibrational properties are evaluated.
- SOC effect on the spectroscopic and vibrational properties is discussed.

This paper investigates the spectroscopic parameters and transition probabilities of 25 low-lying states, which come from the first five dissociation channels of AlC+ cation. The potential energy curves are calculated with the complete active space self-consistent field method, which is followed by the valence internally contracted multireference configuration interaction approach with Davidson correction. Of these 25 states, only the 35Σ−state is repulsive; the c1Σ+, f1Π, and 15Π states have the double well; the first well of c1Σ+ state and the second well of 15Π state are very weakly bound; the first well of c1Σ+ state has no vibrational levels; the 25Π state and the double well of f1Π state have only several vibrational states; the B3Σ−, E3Σ+, D3Π, 15Σ+, 25Σ−, and 15Π states are inverted when the spin-orbit coupling effect is included. The avoided crossings exist between the B3Σ− and 33Σ− states, the c1Σ+ and d1Σ+ states, the f1Π and 31Π states, the 15Π and 25Π states, as well as the 25Π and 35Π states. Core-valence correlation and scalar relativistic corrections are considered. The extrapolation of potential energies to the complete basis set limit is done. The spectroscopic parameters and vibrational levels are determined for all the Λ-S and Ω bound states. The transition dipole moments are calculated. Franck-Condon factors of a great number of electronic transitions are evaluated. On the whole, the spin-orbit coupling effect on the spectroscopic parameters and vibrational levels is small except for very few states. The results determined in this paper could provide some powerful guidelines to observe these states in a spectroscopy experiment.

The PECs of 25 Λ-S states are computed with the CASSCF method followed by the icMRCI + Q approach. The TDMs of 21-pair states are determined by the icMRCI/AV5Z calculations. the spectroscopic parameters, vibrational levels, and transition probabilities of all the bound states are evaluated. The 35Σ- state was repulsive. The c1Σ+, f1Π, and 15Π states have the double well. The first well of c1Σ+ state and the second well of 15Π state are weakly bound. The B3Σ-, E3Σ+, D3Π, 15Σ+, 25Σ-, and 15Π states are inverted with the SOC effect included. The avoided crossings exist between the B3Σ- and 33Σ- states, the c1Σ+ and d1Σ+ states, the f1Π and 31Π states, the 15Π and 25Π states, as well as the 25Π and 35Π states. The first well of c1Σ+ state has no vibrational states. The 25Π state and the double well of f1Π state only have several vibrational states. The SOC effect on the spectroscopic and vibrational properties is small except for the first well of f1Π state, the second well of 15Π state, 25Σ- and 15Δ states. Calculations confirm that almost all the bound states except for the first well of c1Σ+ state could be observerd in a spectroscopy experiment. The spectroscopic and transition properties obtained here could be considered very reliable and could provide some powerful guidelines to observe these states. 160