Formation of complex organic molecules on interstellar CO ices? Insights from computational chemistry simulations. (arXiv:2305.16116v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ferrero_S/0/1/0/all/0/1">Stefano Ferrero</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ceccarelli_C/0/1/0/all/0/1">Cecilia Ceccarelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ugliengo_P/0/1/0/all/0/1">Piero Ugliengo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sodupe_M/0/1/0/all/0/1">Mariona Sodupe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rimola_A/0/1/0/all/0/1">Albert Rimola</a>
Carbon ($^3$P) atom is a reactive species that, according to laboratory
experiments and theoretical calculations, condensates with interstellar ice
components. This fact is of uttermost importance for the chemistry in the
interstellar medium (ISM) because the condensation reaction is barrierless and
the subsequent species formed are still reactive given their open-shell
character. Carbon condensation on CO-rich ices forms the ch{C=C=O}
($^3$$Sigma$$^-$) species, which can be easily hydrogenated twice to form
ketene (H$_2$CCO). Ketene is very reactive in terrestrial conditions, usually
found as an intermediate hard to be isolated in chemical synthesis
laboratories. These characteristics suggest that ketene can be a good candidate
to form interstellar complex organic molecules (iCOMs) via a two-step process,
i.e., its activation followed by a radical-radical coupling. In this work,
reactions between ketene and atomic H, and the OH and NH$_2$ radicals on a
CO-rich ice model have been explored by means of quantum chemical calculations
complemented by kinetic calculations to evaluate if they are favourable in the
ISM. Results indicate that H addition to ketene (helped by tunneling) to form
the acetyl radical (CH$_3$CO) is the most preferred path, as the reactions with
OH and NH$_2$ possess activation energies ($geq$ 9kJ/mol) hard to surmount in
the ISM conditions, unless external processes provide energy to the system.
Thus, acetaldehyde (CH$_3$CHO) and, probably, ethanol (CH$_3$CH$_2$OH)
formation via further hydrogenations are the possible unique operating
synthetic routes. Moreover, from the computed relatively large binding energies
of OH and NH$_2$ on CO ice, slow diffusion is expected, hampering possible
radical-radical couplings with CH$_3$CO. The astrophysical implications of
these findings are discussed considering the incoming James Webb Space
Telescope observations.
Carbon ($^3$P) atom is a reactive species that, according to laboratory
experiments and theoretical calculations, condensates with interstellar ice
components. This fact is of uttermost importance for the chemistry in the
interstellar medium (ISM) because the condensation reaction is barrierless and
the subsequent species formed are still reactive given their open-shell
character. Carbon condensation on CO-rich ices forms the ch{C=C=O}
($^3$$Sigma$$^-$) species, which can be easily hydrogenated twice to form
ketene (H$_2$CCO). Ketene is very reactive in terrestrial conditions, usually
found as an intermediate hard to be isolated in chemical synthesis
laboratories. These characteristics suggest that ketene can be a good candidate
to form interstellar complex organic molecules (iCOMs) via a two-step process,
i.e., its activation followed by a radical-radical coupling. In this work,
reactions between ketene and atomic H, and the OH and NH$_2$ radicals on a
CO-rich ice model have been explored by means of quantum chemical calculations
complemented by kinetic calculations to evaluate if they are favourable in the
ISM. Results indicate that H addition to ketene (helped by tunneling) to form
the acetyl radical (CH$_3$CO) is the most preferred path, as the reactions with
OH and NH$_2$ possess activation energies ($geq$ 9kJ/mol) hard to surmount in
the ISM conditions, unless external processes provide energy to the system.
Thus, acetaldehyde (CH$_3$CHO) and, probably, ethanol (CH$_3$CH$_2$OH)
formation via further hydrogenations are the possible unique operating
synthetic routes. Moreover, from the computed relatively large binding energies
of OH and NH$_2$ on CO ice, slow diffusion is expected, hampering possible
radical-radical couplings with CH$_3$CO. The astrophysical implications of
these findings are discussed considering the incoming James Webb Space
Telescope observations.
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