Nuclear Quantum Effects in H₂ Adsorption Dynamics on a Small Water Cluster Studied with Ring-Polymer Molecular Dynamics Simulations

Molecular hydrogen H₂ is the most abundant molecule in dense interstellar clouds. To understand the role of H₂ in the chemical and physical processes in astrochemical modeling, understanding the sticking probabilities of H₂ to the water ice surface is important. In this work, we calculate H₂ sticking probabilities for a small cluster consisting of eight water molecules using both the quantum ring-polymer molecular dynamics and classical molecular dynamics simulation methods to understand nuclear quantum effects in the H₂ adsorption dynamics. The calculated sticking probabilities decrease with the increase in temperature for both the quantum and classical results. The sticking probabilities calculated using the present small cluster model are comparable with those obtained from the classical simulations using a much larger water ice model. This suggests that the H₂ sticking probability is largely determined by the local nature of the H₂–water interaction. Furthermore, nuclear quantum effects slightly decrease the H₂ sticking probabilities because of a weaker binding energy due to vibrational quantization.