Kavli Affiliate: Lile Wang
|Summary:Molecular hydrogen formation on interstellar dust grains is a key surface process in the interstellar medium, but the redistribution of the recombination energy between the substrate and the nascent molecule remains poorly understood. Here, we use ring-polymer molecular dynamics (RPMD) with a machine-learning force field to investigate energy partitioning during $mathrmH_2$ and $mathrmHD$ formation on graphene at $T=25, 50$ and $100 mathrmK$. We focus on the chemisorbed-H recombination pathway previously identified as the dominant low-temperature channel on bare graphitic surfaces when nuclear quantum effects are included. The desorbing molecule retains the major fraction of the effective surface-mediated released energy, while graphene absorbs a smaller but non-negligible part. This molecular retention fraction is nearly temperature-independent over the investigated range. In contrast, the post-formation molecular kinetic-energy distribution changes more strongly with temperature: rovibrational motion dominates at low temperature, whereas center-of-mass translation becomes increasingly important at $100 mathrmK$. $mathrmH_2$ and $mathrmHD$ exhibit broadly similar total energy retention, with only modest isotope-dependent differences in their internal kinetic-energy partitioning. These results provide an energy-resolved microscopic picture of surface-mediated energy redistribution in $mathrmH_2$/$mathrmHD$ formation, with implications for formation-pumping signatures in high-excitation $mathrmH_2$ lines, vibrationally excited $mathrmH_2$ chemistry, and collisional excitation of coexisting molecules by translationally hot nascent $mathrmH_2$ in cold interstellar gas.| Search Query: arXiv Query: search_query=au:”Wang Lile”&id_list=&start=0&max_results=10Read More