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

Molecular hydrogen H2is the most abundant molecule in dense interstellarclouds. To understand the role of H2in the chemical and physical processes inastrochemical modeling, understanding the sticking probabilities of H2to the water icesurface is important. In this work, we calculate H2sticking probabilities for a small clusterconsisting of eight water molecules using both the quantum ring-polymer moleculardynamics and classical molecular dynamics simulation methods to understand nuclearquantum effects in the H2adsorption dynamics. The calculated sticking probabilitiesdecrease with the increase in temperature for both the quantum and classical results. Thesticking probabilities calculated using the present small cluster model are comparable withthose obtained from the classical simulations using a much larger water ice model. This suggests that the H2sticking probability islargely determined by the local nature of the H2-water interaction. Furthermore, nuclear quantum effects slightly decrease the H2sticking probabilities because of a weaker binding energy due to vibrational quantization.

Automated summary

In this study, the sticking probabilities of H2 on a small cluster consisting of eight water molecules were calculated to understand the nuclear quantum effects in H2 adsorption dynamics. The results show that the sticking probabilities decrease with increasing temperature, and the probabilities obtained from the small cluster model are comparable to those from classical simulations using a larger ice model. This suggests that the H2 sticking probability is mainly determined by the local nature of the H2-water interaction, and nuclear quantum effects slightly decrease the sticking probabilities due to weaker binding energy caused by vibrational quantization.