Water formation on bare grains: When the chemistry on dust impacts interstellar gas
Water formation on bare grains: When the chemistry on dust impacts interstellar gas
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DOI：
10.1051/0004-6361/201014026
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发表时间：
2010-11-01
影响因子：
6.5
通讯作者：
Caselli, P.
中科院分区：
文献类型：
--
作者：
Cazaux, S.;Cobut, V.;Caselli, P.
语境。水和O(2)是形成恒星时冷却致密气体的重要气相成分。正如热岩心观测所揭示的那样，在尘埃颗粒上，H(2)O是冰地幔的重要组成部分，其中正在发生复杂的化学反应。水的形成可能发生在尘埃颗粒表面，并且会影响气相成分。目的。研究 OH、H(2)O、HO(2) 和 H(2)O(2) 等分子的形成及其氘化形式以及 O(2) 和 O(3)，以评估化学在不同天体物理环境中的变化，以及气相如何受到颗粒表面化学的影响。我们使用蒙特卡罗模拟来跟踪裸晶粒上分子的形成以及释放到气相中的分子比例。我们考虑基于气相反应以及化学物质的紫外光解离的表面反应网络。结果。我们表明，颗粒表面化学对气相化学有很大影响，并且对于不同的尘埃颗粒温度，这种化学有很大不同。低温有利于氢化，而较高的温度有利于氧化。此外，紫外光子会解离表面的分子，随后分子会重新形成。形成-破坏循环增加了释放到气相中的物质的数量。我们还确定了在弥漫和密集的云中形成冰的时间尺度，并表明冰仅在屏蔽环境中形成，这一点得到了观测的支持。
Context. Water and O(2) are important gas phase ingredients for cooling dense gas when forming stars. On dust grains, H(2)O is an important constituent of the icy mantle in which a complex chemistry is taking place, as revealed by hot core observations. The formation of water can occur on dust grain surfaces, and can impact gas phase composition.Aims. The formation of molecules such as OH, H(2)O, HO(2) and H(2)O(2), as well as their deuterated forms and O(2) and O(3) is studied to assess how the chemistry varies in different astrophysical environments, and how the gas phase is affected by grain surface chemistry.Methods. We use Monte Carlo simulations to follow the formation of molecules on bare grains as well as the fraction of molecules released into the gas phase. We consider a surface reaction network, based on gas phase reactions, as well as UV photo-dissociation of the chemical species.Results. We show that grain surface chemistry has a strong impact on gas phase chemistry, and that this chemistry is very different for different dust grain temperatures. Low temperatures favor hydrogenation, while higher temperatures favor oxygenation. Also, UV photons dissociate the molecules on the surface, which can subsequently reform. The formation-destruction cycle increases the amount of species released into the gas phase. We also determine the timescales to form ices in diffuse and dense clouds, and show that ices are formed only in shielded environments, as supported by observations.