Chemistry on Rotating Grain Surface: Ro-Thermal Desorption of Molecules from Ice Mantles. (arXiv:1906.11386v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hoang_T/0/1/0/all/0/1">Thiem Hoang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tung_N/0/1/0/all/0/1">Ngo Duy Tung</a>
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.
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.
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