Formation pathways of complex organic molecules: OH^• projectile colliding with methanol ice mantle (CH₃OH)₁₀

Abstract

In this article, we simulated the collisions of an OH• projectile impacting on a methanol cluster formed by ten units of methanol to mimic an ice mantle (CH3OH)10. The chemical processes occurring after the impact were studied through Born-Oppenheimer (ab-initio) molecular dynamics. We focus on collisions with initial kinetic impact energy of 10–22 eV, where the richest chemistry happens. We report the formation mechanisms of stable complex organic molecules (COMs) such as methoxymethanol CH3OCH2OH, formic acid HCOOH, formyl radical HCO, formaldehyde H2CO and its elusive HCOH isomer. We show that CH2(OH)2, •CH2OH or +CH2OH are key intermediates to generate H2CO and other COMs. We compare the outcomes using OH• with those using OH− projectiles. These processes are likely relevant to the production of COMs in astrophysical environments. We discuss its formation mechanism and the astrophysical implications of these chemical pathways in star-forming regions.

Methanediol CH2(OH)2 and hydroxymethyl CH2OH+: key organic intermediates on the path to complex organic molecules

“…This cluster was hit by an OH + projectile mimicking an interstellar dust grain covered only by methanol molecules. Moreover, a comparison of these results was made with the previous process observed after the impact of OH -, OH • , and OH + projectiles (Inostroza et al 2019;Inostroza-Pino et al 2020. Density functional theory calculations under a micro-canonical ensemble (NEV ensemble) were performed with the hybrid functional of Head-Gordon ωB97X-D (Helgaker et al 1990;Uggerud & Helgaker 1992;Bolton et al 1998;McBride et al 2013) and the Pople Basis Set 6-31+g(d,p) (Gordon 1982;Check et al 2001;Borrás-Almenar et al 2001).…”

“…Density functional theory calculations under a micro-canonical ensemble (NEV ensemble) were performed with the hybrid functional of Head-Gordon ωB97X-D (Helgaker et al 1990;Uggerud & Helgaker 1992;Bolton et al 1998;McBride et al 2013) and the Pople Basis Set 6-31+g(d,p) (Gordon 1982;Check et al 2001;Borrás-Almenar et al 2001). As Inostroza-Pino et al did in 2020 and 2021, we divided a sphere symmetrically to obtain 24 initial impact positions (Inostroza-Pino et al 2020). For each hit, the species were in their ground state and the projectile always faced the center of mass of the (CH 3 OH) 10 ice mantle.…”

“…For each hit, the species were in their ground state and the projectile always faced the center of mass of the (CH 3 OH) 10 ice mantle. The initial kinetic impact energies of 10, 12, 15, 18, 20, and 22 eV employed here are the same as those previously used for the OH -, OH • , and OH + projectiles (Inostroza et al 2019;Inostroza-Pino et al 2020.…”

“…A time step of 0.5 femtoseconds (fs) was chosen, to generate a total of 800 steps, allowing a timescale of 400 fs to analyze each trajectory after impact. The variables of energy and impact position were set up, using the ones selected previously (Inostroza-Pino et al 2020Inostroza et al 2019). Throughout this series of articles, the projectile's charge is the only parameter that is modified.…”

Methoxymethanol Formation Starting from CO-Hydrogenation

“…Ultimately, this would provide a pathway towards ribose, a compound of direct biological relevance. In the recent past, several studies have been published focusing on solid-state MM formation pathways through energetic processing of CH 3 OH ice or CH 3 OH-containing ices (Maity et al 2015;Paardekooper et al 2016;Schneider et al 2019;Inostroza-Pino et al 2020). These studies demonstrated that it is possible to form MM under UV light photolysis or upon cosmic rays bombardment.…”