Chemistry on Rotating Grain Surface: Ro-Thermal Desorption of Molecules from Ice Mantles

It is widely believed that water and complex organic molecules (COMs) first form in the ice mantle of dust grains and are subsequently returned into the gas due to grain heating by intense radiation of protostars.

Previous research on the desorption of molecules from the ice mantle assumed that grains are at rest, which is contrary to the fact that grains are suprathermally rotating as a result of their interaction with an anisotropic radiation or gas flow. Toward an era of precision astrochemistry, the effect of grain rotation on surface chemistry must be quantified. In this paper, we study the effect of suprathermal rotation of dust grains spun-up by radiative torques on the desorption of molecules from icy grain mantles around protostars. We show that centrifugal potential energy due to grain rotation reduces the potential barrier of molecules and significantly enhances their desorption rate. We term this mechanism {\it rotational-thermal} or {\it ro-thermal} desorption.

We apply the ro-thermal mechanism for studying the desorption of molecules from icy grains which are simultaneously heated to high temperatures and spun-up to suprathermal rotation by an intense radiation of protostars. We find that ro-thermal desorption is much more efficient than thermal desorption for molecules with high binding energy such as water and COMs. Our results have important implications for understanding the origin of COMs detected in star-forming regions and call for attention to the effect of suprathermal rotation of icy grains to use molecules as a tracer of physical conditions of star-forming regions.

Thiem Hoang, Ngo Duy Tung
(Submitted on 26 Jun 2019)

Comments: 9 figures, 16 pages, to be submitted
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR); Chemical Physics (physics.chem-ph)
Cite as: arXiv:1906.11386 [astro-ph.GA] (or arXiv:1906.11386v1 [astro-ph.GA] for this version)
Submission history
From: Chi-Thiem Hoang
[v1] Wed, 26 Jun 2019 23:36:05 UTC (2,206 KB)
https://arxiv.org/abs/1906.11386
Astrobiology