Dust as interstellar catalyst

Abstract

Context. The presence of dust in the interstellar medium has profound consequences on the chemical composition of regions where stars are forming. Recent observations show that many species formed onto dust are populating the gas phase, especially in cold environments where UV-and cosmic-ray-induced photons do not account for such processes. Aims. The aim of this paper is to understand and quantify the process that releases solid species into the gas phase, the so-called chemical desorption process, so that an explicit formula can be derived that can be included in astrochemical models. Methods. We present a collection of experimental results of more than ten reactive systems. For each reaction, different substrates such as oxidized graphite and compact amorphous water ice were used. We derived a formula for reproducing the efficiencies of the chemical desorption process that considers the equipartition of the energy of newly formed products, followed by classical bounce on the surface. In part II of this study we extend these results to astrophysical conditions. Results. The equipartition of energy correctly describes the chemical desorption process on bare surfaces. On icy surfaces, the chemical desorption process is much less efficient, and a better description of the interaction with the surface is still needed. Conclusions. We show that the mechanism that directly transforms solid species into gas phase species is efficient for many reactions.

Methylacetylene (CH3CCH) and propene (C3H6) formation in cold dense clouds: A case of dust grain chemistry

“…Chemical desorption is a complex mechanism that very likely depends on the species involved. Very recent work by Minissale et al (Minissale et al 2016) proposes a semi empirical model to estimate the efficiency of chemical desorption for particular species. From this model, using the binding energy of methylacetylene on amorphous water?…”

“…ice measured by (Kimber et al 2014) (equal to 2500 K) for methylacetylene and propene, leads to about 1 % of chemical desorption. This efficiency is highly dependent on the binding energy as well as the semi-empirical parameter ε of (Minissale et al 2016) which corresponds to the fraction of kinetic energy retained by the product colliding with the surface. It should be noted that other non-thermal desorption mechanisms, such as cosmic-ray explosive desorption (Ivlev et al 2015) may play a role.…”

Grain Surface Models and Data for Astrochemistry

“…Moving to the multilayer regime, they find that the desorption probability for the O + O recombination reaction drops to negligible values . Expanding their studies to other reaction systems (e.g., CO + H, H 2 CO + H), they determined relatively low reactive desorption rates in the (close-to) sub-monolayer regime ( 10 %, Minissale et al 2016).…”

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

“…Ward et al 2012;He et al 2014;Minissale et al 2016a,b) reported binding energies for oxygen in the range of E B (O) = 1500 − 1800 K. This is significantly higher than the value of E B (O) = 800 K listed in the UMIST 2012 database. We therefore updated the binding energies for oxygen and several other oxygen bearing species with the values listed in Minissale et al (2016b). The new values with their references are given in Table B.2).…”

“…ChRab_SP Notes. The second column shows the values from the UMIST 2012 database (McElroy et al 2013), the third column the updated values from Minissale et al (2016b). References.…”