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PreprintCC BY 4.0arXiv

Binding Energies of Astrophysically Relevant Molecules on CO2 Clusters: Benchmarking and the Donor-Acceptor Origin of Surface-Dependent Binding

  • Aneesa Ahmad
  • Catherine Walsh
  • Stefan Vogt-Geisse
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Abstract

Carbon dioxide (CO2) is among the most abundant interstellar ices and has been observed by JWST in water-rich mixtures and pure CO2 environments. Astrochemical models adopt binding energies (BEs) measured on water ice because few BEs are available for CO2 ice. We calculate BE distributions for twelve adsorbates (N2, CH4, HCl, C2H2, H2S, HF, HCN, H2CO, HCOOH, HNC, CH3OH, H2O) on CO2 clusters containing two to five molecules using DFT calibrated against CCSD(T)/CBS, a coupled-cluster treatment extrapolated to the complete-basis-set limit. Binding strength depends on whether the adsorbate requires the surface to donate a hydrogen bond (H-bond). CO2 can accept an H-bond but cannot donate one, and all six species compared with water ice from Ahmad et al. (2026) bind more weakly on CO2. The ratio of the BE on CO2 to water ice ranges from 0.66 for H2CO and 0.75 for H2O to 0.87 for CH3OH, 0.89 for HCOOH and 0.92 for C2H2. Formaldehyde is predicted to desorb near 57 K from CO2-rich ice, compared with 85 K from water-rich ice, and could contribute to cold gas-phase H2CO. Although the mean binding energies are changing with cluster size for several species, the differences can be traced to local binding interactions likely to remain important in larger ice models. The BEs vary by more than 500 K between sites, while the desorption peaks range from 11 K for CH4 to 132 K for HCOOH. The limited H-bonding capacity of CO2 may favour separation of mixed H2O:CO2 ice into CO2-rich domains.

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Cite

BibTeXRIS
BibTeX
@misc{ahmad2026binding,
  title = {{Binding Energies of Astrophysically Relevant Molecules on CO$_2$ Clusters: Benchmarking and the Donor-Acceptor Origin of Surface-Dependent Binding}},
  author = {Aneesa Ahmad and Catherine Walsh and Stefan Vogt-Geisse},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.12055},
  eprint = {2610.12055},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.12055},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Binding Energies of Astrophysically Relevant Molecules on CO_2 Clusters: Benchmarking and the Donor-Acceptor Origin of Surface-Dependent Binding
AU  - Aneesa Ahmad
AU  - Catherine Walsh
AU  - Stefan Vogt-Geisse
PY  - 2026
DA  - 2026/10/08
PB  - arXiv
DO  - 10.48550/arxiv.2610.12055
UR  - https://arxiv.org/abs/2610.12055
AB  - Carbon dioxide (CO_2) is among the most abundant interstellar ices and has been observed by JWST in water-rich mixtures and pure CO_2 environments. Astrochemical models adopt binding energies (BEs) measured on water ice because few BEs are available for CO_2 ice. We calculate BE distributions for twelve adsorbates (N_2, CH_4, HCl, C_2H_2, H_2S, HF, HCN, H_2CO, HCOOH, HNC, CH_3OH, H_2O) on CO_2 clusters containing two to five molecules using DFT calibrated against CCSD(T)/CBS, a coupled-cluster treatment extrapolated to the complete-basis-set limit. Binding strength depends on whether the adsorbate requires the surface to donate a hydrogen bond (H-bond). CO_2 can accept an H-bond but cannot donate one, and all six species compared with water ice from Ahmad et al. (2026) bind more weakly on CO_2. The ratio of the BE on CO_2 to water ice ranges from 0.66 for H_2CO and 0.75 for H_2O to 0.87 for CH_3OH, 0.89 for HCOOH and 0.92 for C_2H_2. Formaldehyde is predicted to desorb near 57 K from CO_2-rich ice, compared with 85 K from water-rich ice, and could contribute to cold gas-phase H_2CO. Although the mean binding energies are changing with cluster size for several species, the differences can be traced to local binding interactions likely to remain important in larger ice models. The BEs vary by more than 500 K between sites, while the desorption peaks range from 11 K for CH_4 to 132 K for HCOOH. The limited H-bonding capacity of CO_2 may favour separation of mixed H_2O:CO_2 ice into CO_2-rich domains.
ER  -