论文标题
无定形固体水面上H2CO+H的隧道速率常数
Tunneling Rate Constants for H2CO+H on Amorphous Solid Water Surfaces
论文作者
论文摘要
甲醛（H2CO）是在覆盖星际晶粒的冰冷地幔中观察到的最丰富的分子之一。研究其演变可以有助于我们理解各种星际环境中复杂有机分子的形成。在这项工作中，我们使用量子力学/分子力学（QM/mm）模型研究了H2CO产生CH3O，CH2OH的H2CO的氢化反应和氢抽象的氢反应。 H2CO在ASW表面上的结合能的范围从1000至9370 K变化。在结合能和氢化反应的激活能之间没有发现相关性。将Instanton理论与QM/MM建模相结合，我们计算了Langmuir Hinshelwood的速率常数和H+H2CO表面反应的三种产品渠道的Eley Rideal机制降低到59K。我们发现，由于其高激活障碍的高度降低了两个频道，因此可以忽略生产CH2OH的通道CH2OH。 ASW表面影响反应性，有利于形成CH3O（分支比80％），并阻碍H2CO解离为H2+HCO。另外，在所有反应通道中的动力学同位素效应都很强，并且在通道之间差异很大。最后，我们提供了用于天体化学模型中使用的速率常数。
Formaldehyde (H2CO) is one of the most abundant molecules observed in the icy mantle covering interstellar grains. Studying its evolution can contribute to our understanding of the formation of complex organic molecules in various interstellar environments. In this work, we investigated the hydrogenation reactions of H2CO yielding CH3O, CH2OH, and the hydrogen abstraction resulting in H2+HCO on an amorphous solid water (ASW) surface using a quantum mechanics/molecular mechanics (QM/MM) model. The binding energies of H2CO on the ASW surface vary broadly, from 1000 to 9370 K. No correlation was found between binding energies and activation energies of hydrogenation reactions. Combining instanton theory with QM/MM modeling, we calculated rate constants for the Langmuir Hinshelwood and the Eley Rideal mechanisms for the three product channels of H+H2CO surface reactions down to 59 K. We found that the channel producing CH2OH can be ignored, owing to its high activation barrier leading to significantly lower rates than the other two channels. The ASW surface influences the reactivity in favor of formation of CH3O (branching ratio 80%) and hinders the H2CO dissociation into H2+HCO. In addition, kinetic isotope effects are strong in all reaction channels and vary strongly between the channels. Finally, we provide fits of the rate constants to be used in astrochemical models.
