Diffusion activation energy and desorption activation energy for astrochemically relevant species on water ice show no clear relation

Abstract

The activation energy for desorption (Edes) and that for surface diffusion (Esd) of adsorbed molecules on dust grains are two of the most important parameters for the chemistry in the interstellar medium. Although Edes is often measured by laboratory experiments, the measurement of Esd is sparse. Due to the lack of data, astrochemical models usually assume a simple scaling relation, Esd = fEdes, where f is a constant, irrespective of adsorbed species. Here, we experimentally measure Esd for CH4, H2S, OCS, CH3OH, and CH3CN on water-ice surfaces using an ultra-high-vacuum transmission electron microscope (UHV-TEM). Compiling the measured Esd values and Edes values from the literature, we find that the value of f ranges from ~0.2 to ~0.7, depending on the species. Unless f (or Esd) for the majority of species is available, a natural alternative approach for astrochemical models is running multiple simulations, varying f for each species randomly. In this approach, ranges of molecular abundances predicted by multiple simulations, rather than abundances predicted by each simulation, are important. We here run 10,000 simulations of astrochemical models of molecular clouds and protostellar envelopes, randomly assigning a value of f for each species. In the former case, we identify several key species whose Esd most strongly affects the uncertainties of the model predictions; Esd for those species should be investigated in future laboratory and quantum chemical studies. In the latter case, uncertainties in the Esd of many species contribute to the uncertainties in the model predictions.

Accepted for publication in ApJL

References in corpus (6)

• Binding energies: new values and impact on the efficiency of chemical desorption
• Formation of Complex Organic Molecules in Cold Interstellar Environments through non-diffusive grain-surface and ice-mantle chemistry
• A new modified-rate approach for gas-grain chemical simulations
• Sensitivity analysis of grain surface chemistry to binding energies of ice species
• Chemical Variation among Protostellar Cores: Dependence on Prestellar Core Conditions
• Diffusion of CH${}_4$ in amorphous solid water

Cited by in corpus (19)

• Laboratory and Computational Studies of Interstellar Ices
• Surface Diffusion of Carbon Atoms as a Driver of Interstellar Organic Chemistry
• Modelling Deuterated Isotopologues of Methanol toward the Pre-Stellar Core L1544
• Direct Determination of the Activation Energy for Diffusion of OH Radicals on Water Ice
• Enhanced formation of interstellar complex organic molecules on carbon monoxide ice
• Very Large Telescope Observations of Interstellar Comet 3I/ATLAS. II. From Quiescence to Glow: Dramatic Rise of Ni i Emission and Incipient CN Outgassing at Large Heliocentric Distances*
• Processing of hydroxylamine, NH2OH, an important prebiotic precursor, on interstellar ices
• Molecular Mobility of Extraterrestrial Ices: Surface Diffusion in Astrochemistry and Planetary Science
• Determination of the branching ratio of CH${}_3$OH + OH reaction on water ice surface at 10 K
• Astrochemical effect of the fundamental grain surface processes I. The diffusion of grain surface species and the pre-exponential factor
• CO Adsorption Sites on Interstellar Water Ices Explored with Machine Learning Potentials. Binding energy distributions and snowline
• New measurement of the diffusion of carbon dioxide on non-porous amorphous solid water
• Piecing together formic acid isomerism in dark clouds. Detection of cis-formic acid in TMC-1 and astrochemical modeling
• Diffusive vs. non-diffusive paths to interstellar hydrogen peroxide. A machine learning-based molecular dynamics study
• Impact of ice growth on the physical and chemical properties of dense cloud cores
• High deuteration of methanol in L1544
• A sensitivity analysis of interstellar ice chemistry in astrochemical models
• CO Diffusion on Interstellar Amorphous Solid Water: A Computational Study
• Experimental investigation of O2 diffusion and entrapment in interstellar amorphous solid water (ASW)