H2 formation on interstellar grains and the fate of reaction energy
arXiv:2105.06843 · doi:10.3847/1538-4357/ac0142
Abstract
Molecular hydrogen is the most abundant molecular species in the Universe. While no doubts exist that it is mainly formed on the interstellar dust grain surfaces, many details of this process remain poorly known. In this work, we focus on the fate of the energy released by the H formation on the dust icy mantles, how it is partitioned between the substrate and the newly formed H, a process that has a profound impact on the interstellar medium. We carried out state-of-art \textit{ab-initio} molecular dynamics simulations of H formation on periodic crystalline and amorphous ice surface models. Our calculations show that up to two thirds of the energy liberated in the reaction (300 kJ/mol 3.1 eV) is absorbed by the ice in less than 1 ps. The remaining energy (140 kJ/mol 1.5 eV) is kept by the newly born H. Since it is ten times larger than the H binding energy on the ice, the new H molecule will eventually be released into the gas-phase. The ice water molecules within 4 Å~from the reaction site acquire enough energy, between 3 and 14 kJ/mol (360--1560 K), to potentially liberate other frozen H and, perhaps, frozen CO molecules. If confirmed, the latter process would solve the long standing conundrum of the presence of gaseous CO in molecular clouds. Finally, the vibrational state of the newly formed H drops from highly excited states () to low () vibrational levels in a timescale of the order of ps.
13 pages, 7 figures Submitted to ApJ (in press)
References in corpus (5)
- Binding energies of interstellar molecules on crystalline and amorphous models of water ice by ab-initio calculations
- Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
- Chemical desorption versus energy dissipation: insights from ab-initio molecular dynamics of HCO formation
- A New and Simple Approach to Determine the Abundance of Hydrogen Molecules on Interstellar Ice Mantles
- Adsorption of H on Amorphous Solid Water Studied with Molecular Dynamics Simulations
Cited by in corpus (18)
- Where does the energy go during the interstellar NH formation on water ice? A computational study
- Reaction dynamics on amorphous solid water surfaces using interatomic machine learned potentials. Microscopic energy partition revealed from the P + H -> PH reaction
- Quantifying the chemical desorption of HS and PH from amorphous water ice surfaces
- Cracking the Puzzle of CO2 Formation on Interstellar Ices. Quantum Chemical and Kinetic Study of the CO + OH -> CO2 + H Reaction
- CHCN deuteration in the SVS13-A Class I hot-corino. SOLIS XV
- Proposed importance of HOCO chemistry: Inefficient formation of CO from CO and OH reactions on ice dust
- Single-atom catalysis in space: Computational exploration of Fischer Tropsch reactions in astrophysical environments
- Icy molecule desorption in interstellar grain collisions
- Evolution of Fullerenes in Circumstellar Envelopes by Carbon Condensation: Insights from Reactive Molecular Dynamics Simulations
- Synthesis of urea on the surface of interstellar water ice clusters. A quantum chemical study
- A multigrain-multilayer astrochemical model with variable desorption energy for surface species
- Formation of on polycyclic aromatic hydrocarbons under conditions of the ISM: an ab initio molecular dynamics study
- Piecing together formic acid isomerism in dark clouds. Detection of cis-formic acid in TMC-1 and astrochemical modeling
- Astrochemical Inheritance of Terrestrial Planets Water from Local Wet Silicates
- When did the initial mass function become bottom-heavy?
- Off-lattice Microscopic Monte Carlo Modeling of Molecular Hydrogen Formation on Carbonaceous Dust Grains
- Fine-tuning the complex organic molecule formation: sulfur and CO ice as regulators of surface chemistry
- Theoretical computations on the efficiency of acetaldehyde formation on interstellar icy grains