Rotationless radiative lifetimes and transition probabilities of the seven lowest-lying doublet states of the AlO radical

Abstract

In this work, we report the potential energy curves for the X2Π, A2Σ+, B2Σ+, G2Δ, G′2Σ-, C2Π, and D2Σ+ states of the AlO radical and the transition dipole moments between these states. The calculations are performed with the complete active space self–consistent field method, followed by the valence internally contracted multireference configuration interaction approach under the framework of the Born–Oppenheimer approximation. We find that the rotationless radiative lifetimes are in the order of several hundred ns for the B2Σ+ state, several tens of ns for the C2Π state, and several to more than ten ns for the first well of the D2Σ+ state. These lifetimes indicate that the transitions originated from these states easily occur. The rotationless radiative lifetimes are several to several hundred µs for the G2Δ and G′2Σ- states, and in the order of 10 to 100 µs for the A2Σ+ state. The Einstein coefficients of emissions from the B2Σ+–X2Σ+, C2Π–X2Σ+, and C2Π–A2Π systems, as well as from the first well of the D2Σ+ state to the X2Σ+ and A2Π states are very large, suggesting that the transitions from these systems should be able to be measured readily via spectroscopy. The rovibrational constants are first obtained from the analytic potential by numerically solving the rovibrational Schrödinger equation, and then the spectroscopic parameters are evaluated by fitting the vibrational levels. The distributions of the intensity and wavelength of the spectral transitions are new. The radiative lifetimes reported in this work are also new for all vibrational levels of the C2Π, G2Δ and G′2Σ- states, as well as for υ ≥ 1 levels of the C2Π state. The results reported in this study can be used to detect the 26Al16O radical in outer space.