Molecular clouds under the influence of massive stars in the Galactic
  HII region G353.2+0.9
  The Galactic HII region G353.2+0.9 is excited by the massive open cluster
Pismis-24. By analyzing (sub-)mm molecular-line and -continuum we study the
detailed morphology of the gas and dust, as well as their physical parameters
and their variation across the PDR. We observed various molecules and
transitions to derive the physical properties of the molecular gas through line
ratios, and both LTE and non-LTE analyses. The physical properties of the gas
were derived with a Bayesian approach for the non-LTE analysis. Based on the
continuum data at 870 micron, we derived the dust mass and the column density
of H2, and thus the molecular abundances. The total mass of the gas in the
region is ca. 2000 Mo, while that of the dust is ca. 21 Mo. A velocity gradient
in the region suggests that the expansion of the ionized gas is pushing the
molecular gas away from the observer. We unambiguously identify the ionization
front, at the location of which we detect an increase in gas density and
temperature. We find at least 14 clumps at different positions and LSR
velocities. We derive kinetic temperatures in the ranges 11-45 K (CS) and 20-45
K (CN). The H2 number density is typically around 1e5 cm^-3 from CS and few 1e5
cm^-3 from CN, with maxima above 1e6 cm^-3. The abundances of the molecules
observed vary across the region, and appear to be higher in regions further
away from the ionization front.
