Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Destruction of refractory carbon grains drives the final stage of
  proto-planetary disk chemistry   Here we aim to explore the origin of the strong C2H lines to reimagine the
chemistry of protoplanetary disks. There are a few key aspects that drive our
analysis. First, C2H is detected in young and old systems, hinting at a
long-lived chemistry. Second, as a radical, C2H is rapidly destroyed, within
<1000 yr. These two statements hint that the chemistry responsible for C2H
emission must be predominantly in the gas-phase and must be in equilibrium.
Combining new and published chemical models we find that elevating the total
volatile (gas and ice) C/O ratio is the only natural way to create a long
lived, high C2H abundance. Most of the \ce{C2H} resides in gas with a Fuv/n-gas
~ 10^-7 G0 cm^3. To elevate the volatile C/O ratio, additional carbon has to be
released into the gas to enable an equilibrium chemistry under oxygen-poor
conditions. Photo-ablation of carbon-rich grains seems the most straightforward
way to elevate the C/O ratio above 1.5, powering a long-lived equilibrium
cycle. The regions at which the conditions are optimal for the presence of high
C/O ratio and elevated C2H abundances in the gas disk set by the Fuv/n-gas ~
10^-7 G0 cm^3 condition lie just outside the pebble disk as well as possibly in
disk gaps. This process can thus also explain the (hints of) structure seen in
C2H observations.

29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
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The categories of this paper are: eess
17
The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con