The significant role of water in reactions occurring on the surface of interstellar ice grains: Hydrogenation of pure ketene H2C[double bond, length as m-dash]C[double bond, length as m-dash]O ice versus hydrogenation of mixed H2C[double bond, length as m-dash]C[double bond, length as m-dash]O/H2O ice at 10 K - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Physical Chemistry Chemical Physics Année : 2024

The significant role of water in reactions occurring on the surface of interstellar ice grains: Hydrogenation of pure ketene H2C[double bond, length as m-dash]C[double bond, length as m-dash]O ice versus hydrogenation of mixed H2C[double bond, length as m-dash]C[double bond, length as m-dash]O/H2O ice at 10 K

Résumé

Water ice plays an important role in reactions taking place on the surface of interstellar ice grains, ranging from catalytic effects that reduce reaction barrier heights to effects that stabilize the reaction products and intermediates formed, or that favor one reaction pathway over another, passing through water-involvement in the reaction to produce more complex molecules that cannot be formed without water or water-derived fragments H, O and OH. In this context, we have combined experimental and theoretical studies to investigate ketene (CH2CO) + H solid-state reaction at 10 K in the presence and absence of water molecules under interstellar conditions, through H-bombardment of CH2CO and CH2CO/H2O ices. We show in the present study that with or without water, the ketene molecule reacts with H atoms to form four reaction products, namely CO, H2CO, CH4 and CH3CHO. Based on the amounts of CH2CO consumed during the hydrogenation processes, the CH2CO + 2H reaction appears to be more efficient in the presence of water. This underlines the catalytic role of water ice in reactions occurring on the surface of interstellar ice grains. However, if we refer to the yields of reaction products formed during the hydrogenation of CH2CO and CH2CO/H2O ices, we find that water molecules favor the reaction pathway to form CH3CHO and deactivate that leading to CH4 and H2CO. These experimental results are in good agreements with the theoretical predictions that highlight the catalytic effect of H2O on the CH2CO + H reaction, whose potential energy barrier drops from 4.6 kcal mol(-1) (without water) to 3.8 and 3.6 kcal mol(-1) with one and two water molecules respectively.

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Dates et versions

hal-04443301 , version 1 (07-02-2024)

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Mohamad Ibrahim, Jean-Claude Guillemin, Patrick Chaquin, Alexis Markovits, Lahouari Krim. The significant role of water in reactions occurring on the surface of interstellar ice grains: Hydrogenation of pure ketene H2C[double bond, length as m-dash]C[double bond, length as m-dash]O ice versus hydrogenation of mixed H2C[double bond, length as m-dash]C[double bond, length as m-dash]O/H2O ice at 10 K. Physical Chemistry Chemical Physics, 2024, Physical Chemistry Chemical Physics, 26 (5), pp.4200-4207. ⟨10.1039/d3cp04601j⟩. ⟨hal-04443301⟩
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