Events following the giant impact formation of the Moon are thought to have led to volatile depletion and concurrent mass-dependent fractionation of the isotopes of moderately volatile elements (MVE). The detailed processes and conditions surrounding this episode remain obscured and are not unified by a single model for all volatile elements and compounds. Using available data, including new Zn isotope data for eight lunar samples, we demonstrate that the isotopic fractionation of MVE in the Moon is best expressed by nonideal Rayleigh distillation, approaching the fractionation factor α using the reduced masses of the evaporated isotopologs. With these calculations, a best fit for the data is obtained when the lunar MVE isotope data are normalized to ordinary or enstatite chondrites (), rather than a bulk silicate Earth composition. This analysis further indicates that the parent body from which the Moon formed cannot have partitioned S into its core based on S isotope compositions of lunar rocks. The best fit between and modeled nonideal Rayleigh fractionation is defined by a slope that corresponds to a saturation index of 90%4%. In contrast, the older Highland suite is defined by a saturation index of 75%2%, suggesting that the vapor phase pressure was higher during mare basalt eruptions. This provides the first tangible evidence that the Moon was veiled by a thin atmosphere during mare basalt eruption events spanning at least from 3.8 to 3 billion years ago and implies that MVE isotope fractionation dominantly occurred after the Moon had accreted.

月球巨大撞击形成之后的事件被认为导致了中等挥发性元素 (MVE) 同位素的挥发性消耗和同时发生的质量依赖性分馏。围绕这一事件的详细过程和条件仍然模糊不清，并且没有由所有挥发性元素和化合物的单一模型统一。使用现有数据，包括八个月球样本的新 Zn 同位素数据，我们证明了月球中 MVE 的同位素分馏最好通过非理想瑞利蒸馏来表达，使用蒸发同位素的减少质量来接近分馏因子α。通过这些计算，当月球 MVE 同位素数据归一化为普通或顽火球粒陨石时，可以获得最适合的数据（)，而不是块状硅酸盐地球成分。该分析进一步表明，根据月球岩石的 S 同位素组成，形成月球的母体无法将 S 划分到其核心。与建模的非理想瑞利分馏之间的最佳拟合由对应于 90%4% 饱和指数的斜率定义。相比之下，较旧的 Highland 套件的饱和指数为 75%2%，这表明母马玄武岩喷发期间的气相压力更高。这提供了第一个切实的证据，表明至少在 3.8 至 30 亿年前的玄武岩火山喷发事件期间，月球被稀薄的大气层所掩盖，并暗示 MVE 同位素分馏主要发生在月球吸积之后。