Issue 21, 2013

Water formation at low temperatures by surface O2 hydrogenation III: Monte Carlo simulation

Abstract

Water is the most abundant molecule found in interstellar icy mantles. In space it is thought to be efficiently formed on the surfaces of dust grains through successive hydrogenation of O, O2 and O3. The underlying physico-chemical mechanisms have been studied experimentally in the past decade and in this paper we extend this work theoretically, using Continuous-Time Random-Walk Monte Carlo simulations to disentangle the different processes at play during hydrogenation of molecular oxygen. CTRW-MC offers a kinetic approach to compare simulated surface abundances of different species to the experimental values. For this purpose, the results of four key experiments—sequential hydrogenation as well as co-deposition experiments at 15 and 25 K—are selected that serve as a reference throughout the modeling stage. The aim is to reproduce all four experiments with a single set of parameters. Input for the simulations consists of binding energies as well as reaction barriers (activation energies). In order to understand the influence of the parameters separately, we vary a single process rate at a time. Our main findings are: (i) The key reactions for the hydrogenation route starting from O2 are H + O2, H + HO2, OH + OH, H + H2O2, H + OH. (ii) The relatively high experimental abundance of H2O2 is due to its slow destruction. (iii) The large consumption of O2 at a temperature of 25 K is due to a high hydrogen diffusion rate. (iv) The diffusion of radicals plays an important role in the full reaction network. The resulting set of ‘best fit’ parameters is presented and discussed for use in future astrochemical modeling.

Graphical abstract: Water formation at low temperatures by surface O2 hydrogenation III: Monte Carlo simulation

Article information

Article type
Paper
Submitted
09 Jan 2013
Accepted
11 Mar 2013
First published
14 Mar 2013
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2013,15, 8287-8302

Water formation at low temperatures by surface O2 hydrogenation III: Monte Carlo simulation

T. Lamberts, H. M. Cuppen, S. Ioppolo and H. Linnartz, Phys. Chem. Chem. Phys., 2013, 15, 8287 DOI: 10.1039/C3CP00106G

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements