Laboratory Evidence that Methanol-rich Ice Mantles Lower Methyl Formate Binding Energies
- 1University of Virginia
- 2The Hague University of Applied Sciences
Abstract
Complex organic molecules are widely detected in star-forming regions and are important precursors to prebiotic species. Because these molecules are thought to form primarily within icy grain mantles, their desorption is assumed to be regulated by the sublimation of the surrounding H ₂ O ice matrix. However, observations increasingly reveal gas-phase abundances of methyl formate (MF) at temperatures well below the sublimation temperature of water ice ( T ∼ 100 K), challenging this view. To investigate how ice composition and phase influence MF desorption, we present laboratory temperature-programmed desorption measurements of MF from four astrophysically relevant substrates: amorphous and crystalline H ₂ O and CH ₃ OH. Desorption kinetics were analyzed using pre-exponential factors derived from transition-state theory with leading-edge analysis and non-negative least-squares inversion to recover binding-energy distributions. We find that MF binds more weakly to CH ₃ OH ice than to H ₂ O-rich substrates, with representative binding energies of 6247 ± 43 K for amorphous H ₂ O, 6213 ± 38 K for crystalline H ₂ O and 5469 ± 40 K for amorphous CH ₃ OH. MF deposited on crystalline CH ₃ OH exhibits coverage-independent leading edges consistent with multilayer or island desorption, yielding an effective binding energy of 5333 ± 17 K. Enhanced surface mobility and reduced trapping efficiency on methanol ice, combined with weaker MF binding, provide a natural explanation for the early appearance of gas-phase MF observed in star-forming environments, with characteristic desorption temperatures of ∼85 K on CH ₃ OH and ∼95–100 K on H ₂ O. Together, these effects support a two-step thermal desorption pathway in which MF associated with CH ₃ OH-rich ice can be released prior to bulk H ₂ O sublimation.
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BibTeX
@article{gross2026laboratory,
title = {{Laboratory Evidence that Methanol-rich Ice Mantles Lower Methyl Formate Binding Energies}},
author = {Rachel E. Gross and Jeroen Terwisscha van Scheltinga and L. Ilsedore Cleeves and Catherine A. Dukes and Robin T. Garrod and Alexia Simon and Shane Sawyer and Adam Woodson},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/ae9fee},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9fee},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Laboratory Evidence that Methanol-rich Ice Mantles Lower Methyl Formate Binding Energies
AU - Rachel E. Gross
AU - Jeroen Terwisscha van Scheltinga
AU - L. Ilsedore Cleeves
AU - Catherine A. Dukes
AU - Robin T. Garrod
AU - Alexia Simon
AU - Shane Sawyer
AU - Adam Woodson
PY - 2026
DA - 2026/10/05
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae9fee
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ae9fee
AB - Complex organic molecules are widely detected in star-forming regions and are important precursors to prebiotic species. Because these molecules are thought to form primarily within icy grain mantles, their desorption is assumed to be regulated by the sublimation of the surrounding H ₂ O ice matrix. However, observations increasingly reveal gas-phase abundances of methyl formate (MF) at temperatures well below the sublimation temperature of water ice ( T ∼ 100 K), challenging this view. To investigate how ice composition and phase influence MF desorption, we present laboratory temperature-programmed desorption measurements of MF from four astrophysically relevant substrates: amorphous and crystalline H ₂ O and CH ₃ OH. Desorption kinetics were analyzed using pre-exponential factors derived from transition-state theory with leading-edge analysis and non-negative least-squares inversion to recover binding-energy distributions. We find that MF binds more weakly to CH ₃ OH ice than to H ₂ O-rich substrates, with representative binding energies of 6247 ± 43 K for amorphous H ₂ O, 6213 ± 38 K for crystalline H ₂ O and 5469 ± 40 K for amorphous CH ₃ OH. MF deposited on crystalline CH ₃ OH exhibits coverage-independent leading edges consistent with multilayer or island desorption, yielding an effective binding energy of 5333 ± 17 K. Enhanced surface mobility and reduced trapping efficiency on methanol ice, combined with weaker MF binding, provide a natural explanation for the early appearance of gas-phase MF observed in star-forming environments, with characteristic desorption temperatures of ∼85 K on CH ₃ OH and ∼95–100 K on H ₂ O. Together, these effects support a two-step thermal desorption pathway in which MF associated with CH ₃ OH-rich ice can be released prior to bulk H ₂ O sublimation.
SN - 0004-637X
SN - 1538-4357
ER -