Gibson Kevin D, Luo Yuheng, Kang Christopher, Sun Rui, Sibener Steven J
The James Franck Institute and Department of Chemistry, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA.
Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, Hawaii 96822, USA.
J Chem Phys. 2024 May 21;160(19). doi: 10.1063/5.0205984.
In this paper, we present a combined experimental and theoretical study that explored the initial sticking of water on cooled surfaces. Specifically, these ultra-high vacuum gas-surface scattering experiments utilized supersonic molecular beam techniques in conjunction with a cryogenically cooled highly oriented pyrolytic graphite crystal, giving control over incident kinematic conditions. The D2O translational energy spanning 300-750 meV, the relative D2O flux, and the incident angle could all be varied independently. Three different experimental measurements were made. One involved measuring the total amount of D2O scattering as a function of surface temperature to determine the onset of sticking under non-equilibrium gas-surface collision conditions. Another measurement used He specular scattering to assess structural and coverage information for the interface during D2O adsorption. Finally, we used time-of-flight (TOF) measurements of the scattered D2O to determine how energy is exchanged with the graphite surface at surface temperatures above and near the conditions needed for gaseous condensation. For comparison and elaboration of the roles that internal degrees of freedom play in this process, we also did similar TOF measurements using another mass 20 incident particle, atomic neon. Enriching this study are precise molecular dynamics simulations that elaborate on gas-surface energy transfer and the roles of molecular degrees of freedom in gas-surface collisional energy exchange processes. This study furthers our fundamental understanding of energy exchange and the onset of sticking and ultimately gaseous condensation for gas-surface encounters occurring under high-velocity flows.
在本文中，我们展示了一项结合实验与理论的研究，该研究探索了水在冷却表面上的初始附着情况。具体而言，这些超高真空气体 - 表面散射实验利用了超音速分子束技术，并结合了低温冷却的高度取向热解石墨晶体，从而能够控制入射运动学条件。重水（D₂O）的平动能范围为300 - 750毫电子伏特，重水的相对通量以及入射角均可独立变化。进行了三种不同的实验测量。一种测量涉及测量重水散射总量作为表面温度的函数，以确定非平衡气体 - 表面碰撞条件下的附着起始点。另一种测量利用氦镜面散射来评估重水吸附过程中界面的结构和覆盖信息。最后，我们使用散射重水的飞行时间（TOF）测量来确定在高于和接近气态冷凝所需条件的表面温度下，能量如何与石墨表面交换。为了比较和阐述内部自由度在这一过程中所起的作用，我们还使用另一种质量为20的入射粒子——原子氖进行了类似的飞行时间测量。丰富这项研究的还有精确的分子动力学模拟，这些模拟详细阐述了气体 - 表面能量转移以及分子自由度在气体 - 表面碰撞能量交换过程中的作用。这项研究进一步加深了我们对能量交换、附着起始点以及最终对高速流动下气体 - 表面相遇时气态冷凝的基本理解。
