Capture of Hyperthermal CO2 by Amorphous Water Ice via Molecular Embedding

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• 作者：Grant G. Langlois ; Wenxin Li ; K. D. Gibson ; S. J. Sibener
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：December 17, 2015
• 年：2015
• 卷：119
• 期：50
• 页码：12238-12244
• 全文大小：448K
• ISSN：1520-5215

文摘

We present the first study detailing the capture and aggregation of hyperthermal CO₂ molecules by amorphous solid water (ASW) under ultra-high vacuum conditions at 125 K, near the amorphous/crystalline transition. Using time-resolved in situ reflection鈥揳bsorption infrared spectroscopy (RAIRS), CO₂ molecules with translational energies above 3.0 eV are observed to directly embed underneath the vacuum鈥搒olid interface to become absorbed within the ice films despite an inability to adsorb at 125 K; this behavior is not observed for crystalline films. Upon embedding, the mobility of CO₂ within 125 K amorphous ice and the strength of its intermolecular interactions result in its segregation into clusters within the ice films. Tracing the kinetics of CO₂ embedding events under different energetic conditions allows for elucidation of the underlying dynamics, and we draw comparison with other projectiles we have studied to promote generalized conclusions in regard to empirical prediction of a projectile鈥檚 embedding probability. Through application of a classical model of the entrance barrier for projectiles colliding with amorphous ice, we provide direct evidence for a unified connection between embedding probability and projectile momentum; an account of all embedding data measured by our group traces a unified barrier model. This work highlights the interplay between translational energy and momentum accommodation during collisions with ice in high speed gas flows.