Chemical Features in the Circumnuclear Disk of the Galactic Center
  The circumnuclear disk (CND) of the Galactic Center is exposed to many
energetic phenomena coming from the supermassive black hole Sgr A* and stellar
activities. These energetic activities can affect the chemical composition in
the CND by the interaction with UV-photons, cosmic-rays, X-rays, and shock
waves. We aim to constrain the physical conditions present in the CND by
chemical modeling of observed molecular species detected towards it. We
analyzed a selected set of molecular line data taken toward a position in the
southwest lobe of the CND with the IRAM 30m and APEX 12-meter telescopes and
derived the column density of each molecule using a large velocity gradient
(LVG) analysis. The determined chemical composition is compared with a
time-dependent gas-grain chemical model based on the UCL\_CHEM code that
includes the effects of shock waves with varying physical parameters. Molecules
such as CO, HCN, HCO$^+$, HNC, CS, SO, SiO, NO, CN, H$_2$CO, HC$_3$N,
N$_2$H$^+$ and H$_3$O$^+$ are detected and their column densities are obtained.
Total hydrogen densities obtained from LVG analysis range between $2 \times
10^4$ and $1 \times 10^6\,$cm$^{-3}$ and most species indicate values around
several $\times 10^5\,$cm$^{-3}$, which are lower than values corresponding to
the Roche limit, which shows that the CND is tidally unstable. The chemical
models show good agreement with the observations in cases where the density is
$\sim10^4\,$cm$^{-3}$, the cosmic-ray ionization rate is high, $>10^{-15}
\,$s$^{-1}$, or shocks with velocities $> 40\,$km s$^{-1}$ have occurred.
Comparison of models and observations favors a scenario where the cosmic-ray
ionization rate in the CND is high, but precise effects of other factors such
as shocks, density structures, UV-photons and X-rays from the Sgr A* must be
examined with higher spatial resolution data.
