Molecular Dynamics Simulations of Energy Dissipation on Amorphous Solid Water: Testing the Validity of Equipartition.
Molecular Dynamics Simulations of Energy Dissipation on Amorphous Solid Water: Testing the Validity of Equipartition.
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DOI：
10.1021/acsearthspacechem.1c00116
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发表时间：
2021-08-19
影响因子：
3.4
通讯作者：
Cuppen HM
中科院分区：
文献类型：
--
作者：
Fredon A;Groenenboom GC;Cuppen HM
在星际介质中观察到许多不同的分子种类。这些范围从简单的双原子物种到具有多个碳原子的饱和有机分子。假定后一种分子主要在星际尘埃颗粒的表面形成。所有在低星际温度下进行的表面反应都是放热的。它们的放热性可高达几个电子伏特，这与 10 K 时分子的热能相比是相当大的。据推测，这种放热性可用于从颗粒中解吸反应产物。在之前的研究中，我们已经证明平移激发可以导致解吸，而振动和旋转激发在表面产物的解吸中效率要低得多。然而，键形成时振动激发比平移激发更有可能。本研究跟踪表面分子平移、振动或旋转激发时的能量耗散及其转换或缺乏转换为不同的能量贡献。为此，对表面顶部的分子进行了数千次分子动力学模拟，该分子接受了固定量的振动、旋转或平移能量。考虑了三种不同的表面物质：CO2、H2O 和 CH4，涵盖一定范围的结合能、内部自由度数和分子量。观察到振动拉伸之间的能量快速交换，但仅发现了非常有限的旋转或平移激发交换。为了将能量耗散到表面，表面-分子键的激发至关重要。天体化学模型通常假设反应过程后能量的瞬时均分，以估计化学解吸的可用能量。根据目前的研究，我们得出结论，这种假设是不合理的。
Many different molecular species have been observed in the interstellar medium. These range from simple diatomic species to saturated organic molecules with several carbon atoms. The latter molecules are assumed to be formed predominantely on the surface of interstellar dust grains. All surface reactions that can proceed under the low interstellar temperatures are exothermic. Their exothermicity can be as high as a few electron volts, which is considerable compared to the thermal energy of the molecules at 10 K. It is postulated that this exothermicity can be used for the desorption of reaction products from the grain. In previous studies, we have shown that translational excitation can lead to desorption, whereas vibrational and rotational excitations are much less efficient in the desorption of surface products. Vibrational excitation is however much more likely upon bond formation than translational excitation. The present study follows energy dissipation upon translational, vibrational, or rotational excitation of admolecules on a surface and its conversion, or lack thereof, to different energy contributions. To this end, thousands of molecular dynamics simulations were performed with an admolecule on top of a surface that received a fixed amount of energy, vibrational, rotational, or translational. Three different surface species have been considered, CO2, H2O, and CH4, spanning a range in binding energies, the number of internal degrees of freedom, and molecular weights. A fast exchange of energy between vibrational stretches is observed, but only very limited exchange to rotational or translation excitation has been found. For the dissipation of energy to the surface, excitation of the surface–admolecule bond is critical. Astrochemical models often assume instantaneous equipartition of energy after a reaction process to estimate the amount of available energy for chemical desorption. Based on the present study, we conclude that this assumption is not justified.
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影响因子：
4.4
作者：
LEE, TJ;MARTIN, JML;TAYLOR, PR
通讯作者：
TAYLOR, PR
影响因子：
4.9
作者：
Pantaleone, Stefano;Enrique-Romero, Joan;Rimola, Albert
通讯作者：
Rimola, Albert
影响因子：
4.9
作者：
Fredon, A.;Lamberts, T.;Cuppen, H. M.
通讯作者：
Cuppen, H. M.
影响因子：
4.1
作者：
PLIMPTON, S
通讯作者：
PLIMPTON, S
影响因子：
6.3
作者：
ZHU, SB;ROBINSON, GW
通讯作者：
ROBINSON, GW