Contribution Contributed Talk
Formation of acetaldehyde on icy grain particles? Insights from quantum chemical calculations
- Dr. Albert RIMOLA
- Dr. Albert RIMOLA (Universitat Autònoma de Barcelona)
About 200 molecular species were detected in the ISM. Some of them are complex organic molecules (COMs), molecules with more than 6 atoms containing one or multiple C atoms. Some COMs can reach a certain degree of complexity and can have a prebiotic relevance. Knowing whether COMs contributed or not to the chemical evolution needed for the emergence of life is one of the open questions in the origin of life studies. Two classes of models are invoked to explain the interstellar synthesis of COMs. One advocates formation of COMs on the grain surfaces (Öberg 2016; Garrod et al. 2008), in which dissociation of frozen hydrogenated species gives radicals, which in turn recombine to form COMs. The other postulates that they form via gas-phase reactions (Caselli et al. 1993, Taquet et al. 2016), in which the frozen hydrogenated species desorb into the gas phase and react with other gaseous species to form COMs through a series of gas-phase processes. The problem in knowing which of the two models is correct and in which conditions each model is applicable mostly comes from a dramatic lack of experimental and theoretical data of gas-phase and on-surface reactions. This communication focuses on the formation of acetaldehyde as a test case of COM formation by reaction of CH$_3$ + HCO $\longrightarrow$ CH$_3$CHO on grain surfaces simulated by means of quantum chemical. The water ice surface is modelled by a cluster approach consisting of 18 H$_2$O molecules. Results indicate that, on surfaces, other processes are competitive reactive channels. The most predominant one is formation of CH$_4$ + CO (see Figure) occurring through a set of H transfers mediated by the water surface (Enrique-Romero et al. 2016). However, these are preliminary results and discussion on how more realistic surface models can affect the outcome of the simulations will be presented.
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