Formation of complex organic molecules in ice mantles: An ab initio molecular dynamics study

¹ Universidad Autónoma de Chile, Facultad de Ingeniería, Núcleo de Astroquímica & Astrofísica, Av. Pedro de Valdivia 425, Providencia, Santiago, Chile
e-mail: natalia.inostroza@uautonoma.cl
² Universidad de Chile, Facultad de Ciencias Físicas y Matemáticas, Departamento de Astronomía, Camino el Observatorio 1515, Las Condes, Santiago, Chile
³ Center for Astrochemical Studies, Max Planck Institute for Extraterrestial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
⁴ Consejo Superior de Investigaciones Cientificas CSIC-IFF, Serrano 121, Madrid, Spain
⁵ Universidad Andrés Bello, Doctorado en Fisicoquímica Molecular, República 275, Santiago, Chile
⁶ Universidad de Chile, Facultad de Ciencias, Departamento de Física, Av. Las Palmeras 3425, Ñuñoa, Santiago, Chile
⁷ Centro para el Desarrollo de la Nanociencia y la Nanotecnología (CEDENNA), Avda. Ecuador 3493, Santiago 9170124, Chile

Received: 6 August 2018
Accepted: 10 July 2019

Abstract

We present a detailed simulation of a dust grain covered by a decamer of (CH₃OH)₁₀-ice-mantle, bombarded by an OH⁻ closed-shell molecule with kinetic energies from 10–22 eV. The chemical pathways are studied through Born-Oppenheimer (ab initio) molecular dynamics. The simulations show that methanol ice-mantles can be a key generator of complex organic molecules (COMs). We report the formation of COMs such as methylene glycol (CH₂(OH)₂) and the OCH₂OH radical, which have not been detected yet in the interstellar medium (ISM). We discuss the chemical formation of new species through the reaction of CH₃OH with the hydroxyl projectile. The dependence of the outcome on the kinetic energy of the projectile and the implications for the observation and detection of these molecules might explain why the methoxy radical (CH₃  ⋅ ) has been observed in a wider range of astrophysical environments than the hydroxymethyl (CH₂OH ⋅) isomer. Because of the projectile kinetic energies required for these reactions to occur, we suggest that these processes are likely relevant in the production of COMs in photodissociation and shock regions produced by high-velocity jets and outflows from young stellar objects.