Energy Partitioning in Dust-catalyzed H2 and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects
Abstract
Molecular hydrogen formation on interstellar dust grains is a key surface process, but the partitioning of 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 H2 and HD formation on graphene at T=25 K, 50 K and 100 K, focusing 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 approximately 84-87% of the effective released energy, with only weak variation across the three velocity-initialization temperatures under the present sampling protocol. Within the retained molecular energy, rovibrational motion dominates at 25 K, whereas center-of-mass translation becomes increasingly important at 100 K. H2 and HD show similar total energy retention, with modest isotope-dependent differences in their internal partitioning. The effective joint rovibrational distributions show a modest positive association between vibrational and rotational excitation. Purely radiative cascade calculations in the optically thin, collision-free limit yield formation-pumping spectra at all three temperatures. From 25 to 100 K, the rovibrational fraction of the emitted energy decreases from approximately 43% to 28% for H2 and from 41% to 28% for HD, while the strongest lines remain in similar wavelength regions. These results provide an energy-resolved microscopic picture of surface-mediated energy redistribution and formation pumping in H2/HD formation on graphene.
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BibTeX
@misc{yang2026energy,
title = {{Energy Partitioning in Dust-catalyzed $\mathrmH_2$ and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects}},
author = {Xiaolong Yang and Lile Wang and Di Li and Shenzhen Xu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.13843},
eprint = {2608.13843},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.13843},
}
RIS
TY - UNPB
TI - Energy Partitioning in Dust-catalyzed H_2 and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects
AU - Xiaolong Yang
AU - Lile Wang
AU - Di Li
AU - Shenzhen Xu
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2608.13843
UR - https://arxiv.org/abs/2608.13843
AB - Molecular hydrogen formation on interstellar dust grains is a key surface process, but the partitioning of 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 H2 and HD formation on graphene at T=25 K, 50 K and 100 K, focusing 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 approximately 84-87% of the effective released energy, with only weak variation across the three velocity-initialization temperatures under the present sampling protocol. Within the retained molecular energy, rovibrational motion dominates at 25 K, whereas center-of-mass translation becomes increasingly important at 100 K. H2 and HD show similar total energy retention, with modest isotope-dependent differences in their internal partitioning. The effective joint rovibrational distributions show a modest positive association between vibrational and rotational excitation. Purely radiative cascade calculations in the optically thin, collision-free limit yield formation-pumping spectra at all three temperatures. From 25 to 100 K, the rovibrational fraction of the emitted energy decreases from approximately 43% to 28% for H2 and from 41% to 28% for HD, while the strongest lines remain in similar wavelength regions. These results provide an energy-resolved microscopic picture of surface-mediated energy redistribution and formation pumping in H2/HD formation on graphene.
ER -