The radiative association process for the formation of magnesium oxide (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⁺, |${\rm X}^1\Sigma ^+\, \rightarrow \, {\rm A}^1\Pi$|⁠, D¹Δ → A¹Π, a³Π → e³Σ⁻, |${\rm X}^1\Sigma ^+\, \rightarrow \, {\rm X}^1\Sigma ^+$|⁠, 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 10–10 000 K and the results are found to vary from 4.69 |$\times \, 10^{-16}$| to 6.27 |$\times \, 10^{-14}$| cm³ s⁻¹. For temperatures lower than around 693 K, 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.

中文翻译：

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辐射缔合形成的MgO

氧化镁（MgO）的辐射缔合过程可能很重要，因为它在低密度和粉尘少的化学环境中经常发生。在这项工作中，横截面和速率系数为A ¹ Π→X ¹ Σ ⁺，| $ {\ RM X} ^ 1 \西格玛^ + \，\ RIGHTARROW \ {\ RM A} ^ 1 \裨$ |⁠，d ¹ Δ→阿¹ Π，一个³ Π→ë ³ Σ ^-，| $ {\ RM X} ^ 1 \西格玛^ + \，\ RIGHTARROW \ {\ RM X} ^ 1 \西格玛^ + $ |⁠，和A ¹ Π→一个¹理论上估计形成MgO的Π辐射缔合过程。通过使用直接贡献的半经典方法和Breit-Wigner理论作为共振贡献的补充，可以得出不同状态之间跃迁的横截面。对于相同状态之间的过渡，使用了量子力学方法。然后，从横截面获得10–10000 K温度范围内的速率系数，结果发现其变化范围为4.69 | $ \ times \，10 ^ {-16} $ |。到6.27 | $ \ times \，10 ^ {-14} $ | cm ³  s ^-1。为温度约693ķ低于，速率系数为A ¹ Π→X ¹ Σ ⁺该工艺占主导地位，这表明该工艺是在低温下生产MgO的最有效方法。然而，对于d的速率系数¹ Δ→阿¹ Π过程经历随温度升高而迅速增加，并成为在较高温度下占主导地位。对于其他过程，其速率系数比上述两个过程的速率系数低几个数量级。该结果可用于进一步研究低密度和热气体中靠近已演化的富氧恒星光球的MgO的形成和演化。