Computer simulations of water interactions with low-coordinated forsterite surface sites: Implications for the origin of water in the inner solar system
Computer simulations of water interactions with low-coordinated forsterite surface sites: Implications for the origin of water in the inner solar system
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DOI：
10.1016/j.epsl.2010.10.019
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发表时间：
2010-11-15
影响因子：
5.3
通讯作者：
de Leeuw, N. H.
中科院分区：
文献类型：
--
作者：
King, H. E.;Stimpfl, M.;de Leeuw, N. H.
在吸积过程中，水在分形尘埃颗粒上的吸附被认为是岩石行星的一个可能的水来源。我们使用计算机模拟来研究镁橄榄石尘埃颗粒化学吸附的可行性，通过研究离解水在化学计量比表面和缺陷表面的吸附。缺陷用不同镁橄榄岩表面的台阶、角位和空位来模拟。结果表明，水在化学计量比(100)面上发生解离，而在化学计量比(010)面上没有发生解离。然而，台阶和拐角的解离吸附释放的能量表明，如果存在这些特征，化学吸附在(010)表面的势垒将是有利的。所有被研究的表面上的台阶和角落都产生了低配位的镁位置，因此具有高度的活性，有利于水的解离。台阶之间的梯田大小对最终能量的影响有限，尽管较小的梯田在角落产生了更多的活性镁位置。用一个简单的Langmuir模型和我们模拟得到的能量数据来检验在适用于吸积盘的温度和压力条件下水吸附的有效性。这项研究的发现表明，即使在低分压的情况下，水也会强烈吸附在镁橄榄岩的分形表面上，这表明在行星吸积过程中，水可能会被保留下来。(C)2010爱思唯尔B.V.保留所有权利。
Adsorption of water to fractal dust grains during accretion has been proposed as a possible source of water for rocky planets. We have used computer simulations to study the feasibility of chemisorption onto forsterite dust grains by investigating the adsorption of dissociated water to stoichiometric and defective surfaces. Defects were modeled using steps, corner sites and vacancies on different forsterite surfaces. Our results show that water dissociation is expected on the stoichiometric (100) surface but not on the stoichiometric (010) surface. However, the energies released by dissociative adsorption at steps and corners indicate that the energetic barrier to chemisorption on the (010) surface would be favorable if these features were present. Steps and corners on all surfaces studied produced Mg sites that have low coordination and thus were highly reactive, favoring the dissociation of water. Terrace size between the steps was shown to have a limited effect on the final energies, although smaller terraces created more reactive Mg sites at corners. A simple Langmuir model was used with the energetic data from our simulations to examine the effectiveness of water adsorption at temperature and pressure conditions applicable to the accretion disk. The findings of this study suggest that water would be strongly chemisorbed at fractal forsterite surfaces even at low partial pressures suggesting that water could be retained during planetary accretion. (C) 2010 Elsevier B.V. All rights reserved.