RT info:eu-repo/semantics/article
T1 Revisiting the OH + H2 → H2O + H reaction at the molecular level: the plausible catalytic role of ice in its own reconstruction
A1 Pauzat, F.
A1 Markovits, A.
A1 Ellinger, Y.
A1 Redondo Cristóbal, María del Pilar
A1 ellinger
K1 astrochemistry
K1 ISM: molecules
K1 ISM: abundances
K1 molecular processes
K1 solid state: volatile
AB Context. In spite of the permanent damage suffered from the radiation field (cosmic rays, X-rays, and intense UV-visible radiations), interstellar grains are still covered by ices mantles whose role in interstellar chemistry is well beyond any doubt. This clearly means that the destruction of the ice cover has to be counterbalanced by efficient reconstruction mechanisms.Aims. Our goal is to determine whether the ice, which is still present after irradiation, has a catalytic role in the OH + H2 → H2O + H reaction for its own reconstruction. We focus on the three plausible reaction paths depending on the way reactants OH or H2 are adsorbed at the ice surface.Methods. Calculations were performed in both cluster and solid state approaches, using ab-initio post Hartree-Fock methods for small systems, standard density functional theory (DFT) for larger clusters, and periodic solid state DFT with specific formalisms accounting for weak interactions in systems of infinite dimensions.Results. Although the end product is the same, that is namely the reconstruction of one H2O on the subjacent ice, three different reaction paths are found depending on whether H2 reacts with adsorbed OH(ads), wether OH reacts with adsorbed H2(ads) or wether both OH(ads) and H2(ads) are adsorbed on the ice before reacting. In the first case, there is an activation barrier of ~6 kcal mol−1, requiring the tunneling effect for the reaction to proceed, which is in agreement with preceding studies. In the second case, the reaction is a barrierless process leading to the direct reconstruction of the ice. In the third case, the double adsorption increases the activation barrier due to the lowering of the starting energy. This is found regardless of the dimension of the supporting ice aggregates.Conclusions. Icy grain surfaces play a critical role for their own reconstruction in cold, dense interstellar clouds. The prevalence of tunneling over the direct mechanism should strongly depend on the temperature and local environment.
PB EDP Sciences
SN 0004-6361
YR 2021
FD 2021
LK https://uvadoc.uva.es/handle/10324/65166
UL https://uvadoc.uva.es/handle/10324/65166
LA eng
NO Astronomy & Astrophysics, 646 (2021) A163
NO Producción Científica
DS UVaDOC
RD 08-ago-2024