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The radiative association process for the formation of MgO may be of great importance due to its frequent occurrence in the low-density and dust-poor astrochemical environments. In this work, the cross sections and rate coefficients for the A1Π → X1Σ+, X1Σ+ → A1Π, D1Δ → A1Π, a3Π → e3Σ−, X1Σ+ → X1Σ+ and A1Π → A1Π radiative association processes of forming MgO are theoretically estimated. The cross sections for the transitions between the different states are obtained by using the semiclassical method for direct contributions and the Breit-Wigner theory as a complement for resonance contributions. For the transitions between the same states, the quantum mechanical method is used. The rate coefficients are then obtained from the cross sections for the temperatures in the range of 10-10000K and the results are found to vary from 4.6 × 10−16 cm3s−1 to 6.27 times 10−14 cm3s−1. For temperatures lower than around 693K, the rate coefficients for the A1Π → X1Σ+ process are dominant, which indicates this process is the most efficient way of producing MgO at low temperatures. However, the rate coefficients for the D1Δ → A1Π process go through a rapid increase with increasing temperature and become dominant at higher temperatures. For other processes, their rate coefficients are several orders of magnitude lower than those for the two processes mentioned above. The results can be used to further investigate the formation and evolution of MgO in low-density and hot gas close to the photosphere of evolved oxygen-rich stars.

Photodissociation processes are of great importance for modeling interstellar chemistry since it is a key destruction pathway for small molecules. Here, we present a detailed ab initio study of AlH photodissociation. Potential energy curves and transition dipole moments for AlH are obtained by using the internally contracted multireference configuration interaction method and the Davidson correction (icMRCI+Q), as well as the aug-cc-pV6Z basis set. Except for the X1Σ+, A1Π, and C1Σ+ states, five higher excited 31Σ+, 21Π, 31Π, 41Σ+, and 41Π states are considered in order to investigate the photodissociation pathways in the vacuum ultraviolet region. State-resolved cross sections of transitions from all the rovibrational levels of the X1Σ+ state to seven singlet excited states are computed for photon wavelengths ranging from 500 Å to the threshold. Photodissociation cross sections in local thermal equilibrium (LTE) are obtained at temperatures from 500 to 10,000 K. Applications of the LTE cross sections to compute photodissociation rates in the standard interstellar radiation field and blackbody radiation field are briefly discussed.

Radiative association may be a key pathway for the formation of aluminium monoxide (AlO) in diffuse interstellar clouds, especially for the oxygen-rich asymptotic giant branch (AGB) stars. In this work, we investigated the radiative association of AlO by the collision of the aluminum and oxygen atoms in their electronic ground states, which is thought to be the most probable radiative association process. Firstly, the potential energy curves for twelve electronic states and the dipole moments between these states were calculated by the state-of-the-art ab initio methodology. Then the cross sections and rate coefficients for the radiative association of AlO were computed for the temperatures in the range of 10 - 10000 K. The total rate coefficients are of the order of 2.73 × 10−19 − 1.14 × 10−16 cm3s−1, and the A2Π → X2Σ+, 12Δ → A2Π, 12Π → X2Σ+ and 22Σ− → A2Π transitions play a key role. The calculated results can be used to investigate the chemical evolution of dust formation in the photospheres of the oxygen-rich AGB stars.