Molecules in the Circumnuclear Disk of the Galactic Center
  Within a few parsecs around the central Black Hole Sgr A*, chemistry in the
dense molecular cloud material of the circumnuclear disk (CND) can be affected
by many energetic phenomena such as high UV-flux from the massive central star
cluster, X-rays from Sgr A*, shock waves, and an enhanced cosmic-ray flux.
Recently, spectroscopic surveys with the IRAM 30 meter and the APEX 12 meter
telescopes of substantial parts of the 80--500 GHz frequency range were made
toward selected positions in and near the CND. These datasets contain lines
from the molecules HCN, HCO$^+$, HNC, CS, SO, SiO, CN, H$_2$CO, HC$_3$N,
N$_2$H$^+$, H$_3$O$^+$ and others. We conduct Large Velocity Gradient analyses
to obtain column densities and total hydrogen densities, $n$, for each species
in molecular clouds located in the southwest lobe of CND. The data for the
above mentioned molecules indicate 10$^5\,$cm$^{-3} \lesssim n
<10^6\,$cm$^{-3}$, which shows that the CND is tidally unstable. The derived
chemical composition is compared with a chemical model calculated using the
UCL\_CHEM code that includes gas and grain reactions, and the effects of shock
waves. Models are run for varying shock velocities, cosmic-ray ionization
rates, and number densities. The resulting chemical composition is fitted best
to an extremely high value of cosmic-ray ionization rate $\zeta \sim
10^{-14}\,$s$^{-1}$, 3 orders of magnitude higher than the value in regular
Galactic molecular clouds, if the pre-shock density is $n=10^5\,$cm$^{-3}$.
