Interstellar formaldehyde (CH2O) is a primordial organic molecule in the interstellar medium. Whereas the gas-phase reaction of CH3 + O ? CH2O + H is inefficient1 due to the low production of CH3, laboratory experiments based on H-bombardment of CO ices have produced CH2O very efficiently.2 Here, a quantum chemical description based on DFT methods for the formation of CH2O via successive H additions to CO (CO ? HCO ? H2CO) is addressed, both in gas-phase and on the surfaces of water clusters ((H2O)n, n =18 and 32). Results clearly show that, on the water surfaces, the energy barriers decrease due to the polarizing effects exerted by water on the C-O bond as a consequence of the H-bonds between CO and the water ice surfaces. An alternative route to the CH2O formation has also been addressed in light of the fact that dust grains can capture free electrons from interstellar gas (104-105e m-3), becoming negatively-charged particles.3 Here, results on the reaction between singly negatively charged water clusters ((H2O)n-�, n = 14, 20 and 24) and HCO+ are addressed. Two competitive processes have been considered: i) capture of the excess of electron of the water cluster by HCO+ to form HCO; ii) proton transfer from HCO+ to ((H2O)n-�) to yield CO and [(H3O�)(H2O)n-1]. Results calculated at the MP2 level with large basis sets4 indicate that the first process is the most favorable one, opening an unexplored reactive channel for the formation of CH2O in the interstellar medium.1. W. D. Watson, Acc. Chem. Res., 1977, 10 , 221-226.2. N. Watanabe and A. Kouchi, Progress in Surface Science, 2008, 83 , 439-489.3. A. Evans, The Dusty Universe, Ellis Horwood, New York, 1993.4. J. M. Herbert and M. Head-Gordon, J. Phys. Chem. A, 2005, 109 , 5217-5229.

Polarizing and electrons charge effects for the formation of CH<sub>2</sub>O on surfaces of water icy dust particles

247th National Meeting (2014)

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Polarizing and electrons charge effects for the formation of CH2O on surfaces of water icy dust particles

Polarizing and electrons charge effects for the formation of CH₂O on surfaces of water icy dust particles