Direct Measurements of Activation Energies for Surface Diffusion of CO and CO2 on Amorphous Solid Water Using In Situ Transmission Electron Microscopy
Direct Measurements of Activation Energies for Surface Diffusion of CO and CO2 on Amorphous Solid Water Using In Situ Transmission Electron Microscopy
复制标题
DOI：
10.3847/2041-8213/ab78a2
复制
发表时间：
2020-03-01
影响因子：
7.9
通讯作者：
Watanabe, Naoki
中科院分区：
文献类型：
--
作者：
Kouchi, Akira;Furuya, Kenji;Watanabe, Naoki
吸附分子在无定形固体水（ASW）上的表面扩散活化能（E-sd）的重要性已被广泛讨论在低温下ASW上的化学反应。然而，在以前的工作中，E-sd没有直接测量，而是从间接实验估计。在化学网络计算中已经假设E-sd在分子的解吸能的0.3和0.8之间。获得E-sd的直接测量值仍然很重要。我们进行了原位观察的沉积过程中的CO和CO2 ASW上使用透射电子显微镜（TEM）和推断的E-SD的CO和CO2 ASW上分别为350 - 50和1500 - 100 K。CO的E-sd值约为CO在ASW上的总吸附能的0.3，即，远小于化学网络计算中假设的，其中相应的数值为575 K，假设约为0.5的解吸能。我们证明，TEM是非常有用的，不仅用于观测冰，而且用于测量一些物理性质，是相关的天体化学和天体物理。利用本研究中测量的CO的E-sd（350 K），我们更新了Furuya等人的化学网络模型，证实了在分子云演化的初始阶段，CO + OH -> CO2 + H反应可以有效地形成CO2。
The importance of the activation energy of surface diffusion (E-sd) of adsorbed molecules on amorphous solid water (ASW) has been widely discussed in terms of chemical reactions on ASW at low temperatures. However, in previous work, E-sd has not been measured directly but estimated from indirect experiments. It has been assumed in chemical network calculations that E-sd is between 0.3 and 0.8 of the desorption energies of a molecule. It remains important to obtain direct measurements of E-sd. We performed in situ observations of the deposition process of CO and CO2 on ASW using transmission electron microscopy (TEM) and deduced the E-sd of CO and CO2 on ASW to be 350 50 and 1500 100 K, respectively. The value of E-sd of CO is approximately 0.3 of the total adsorption energy of CO on ASW, i.e., much smaller than assumed in chemical network calculations, where the corresponding figure is 575 K, assuming approximately 0.5 of the desorption energy. We demonstrated that TEM is very useful not only for the observation of ices but also for the measurement of some physical properties that are relevant in astrochemistry and astrophysics. Using the E-sd of CO measured in the present study (350 K), we have updated the chemical network model of Furuya et al., confirming that CO2 could be efficiently formed by the reaction CO + OH -> CO2 + H in the initial stages of the evolution of molecular clouds.