Non-transition metal oxides, including major minerals of the early Solar System, are known to evaporate decomposing into multiple gas molecules, while maintaining their stoichiometric compositions (dissociative congruent evaporation). Here, we derived the absolute rate of this type of evaporation using the transition state theory. In our modified transition state theory, the activation energy closely corresponds to the average energy of the molecules at the transition state, reflecting the degree of decomposition at the potential energy barrier along the reaction coordinate of evaporation. By comparing the theoretical and experimental evaporation rates for the reaction MgO (s) → Mg (g) + O (g), we found that there is an activation barrier close to the product side (i.e., “late” barrier) where the decomposition is almost achieved. The present theory is advantageous to the Hertz–Knudsen equation, which is essentially formulated as the evaporation rate in equilibrium based on the detailed balance, in that it describes dissociative congruent evaporation as a non-equilibrium process and thus provides the link between the experiments and the reaction dynamics.

中文翻译：

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基于过渡态理论的离解同成分蒸发动力学

已知非过渡金属氧化物，包括早期太阳系的主要矿物，会蒸发分解成多个气体分子，同时保持其化学计量组成（离解同成分蒸发）。在这里，我们使用过渡态理论推导了此类蒸发的绝对速率。在我们改进的过渡态理论中，活化能与过渡态分子的平均能量紧密对应，反映了沿蒸发反应坐标在势能垒处的分解程度。通过比较 MgO (s) → Mg (g) + O (g) 反应的理论和实验蒸发速率，我们发现靠近产物侧存在一个活化势垒（即“晚期”势垒），其中分解发生已经快要实现了。本理论有利于赫兹-克努森方程，该方程本质上是基于详细平衡的平衡蒸发速率，因为它将解离同成分蒸发描述为非平衡过程，从而提供了实验和蒸发之间的联系。反应动力学。