Ring-polymer Molecular Dynamics Simulation for the Adsorption of H 2 on Ice Clusters (H 2 O) n (n=8, 10, and 12).

In the interstellar medium, the H ₂ adsorption and desorption on the solid water ice are crucial for chemical and physical processes. We have recently investigated the probabilities of H ₂ sticking on the (H ₂ O) ₈ ice, which has quadrilateral surfaces. We have extended the previous work using classical MD and ring-polymer molecular dynamics (RPMD) simulations to the larger ice clusters, (H ₂ O) ₁₀ and (H ₂ O) ₁₂ , which have pentagonal and hexagonal surfaces, respectively. The H ₂ sticking probabilities decreased as the temperature increased for both cluster cases, whereas the cluster-size-independent profiles were observed. It is thought that the size independence of the probabilities is qualitatively understood from the similar binding energies for all the three cluster systems. Furthermore, the RPMD sticking probabilities are smaller than the classical ones because of the reduction in the binding energies owing to nuclear quantum effects, such as vibrational quantization.
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