Using the 15-m Swedish ESO Sub-millimeter Telescope ( SEST ) , CO , HCN , and HCO ^ { + } observations of the galactic star-forming region NGC 6334 FIR II are presented , complemented by [ C i ] ^ { 3 } P _ { 1 } - ^ { 3 } P _ { 0 } and ^ { 3 } P _ { 2 } - ^ { 3 } P _ { 1 } data from the Atacama Pathfinder Experiment ( APEX 12-m telescope ) .
Embedded in the extended molecular cloud and associated with the H ii region NGC 6334–D , there is a molecular “ void ” .
[ C i ] correlates well with ^ { 13 } CO and other molecular lines and shows no rim brightening relative to molecular cloud regions farther off the void .
While an interpretation in terms of a highly clumped cloud morphology is possible , with photon dominated regions ( PDRs ) reaching deep into the cloud , the data do not provide any direct evidence for a close association of [ C i ] with PDRs .
Kinetic temperatures are \sim 40–50 K in the molecular cloud and \ga 200 K toward the void .
CO and [ C i ] excitation temperatures are similar .
A comparison of molecular and atomic fine structure line emission with the far infrared and radio continuum as well as the distribution of 2.2 \mu m H _ { 2 } emission indicates that the well-evolved H ii region expands into a medium that is homogeneous on pc-scales .
If the H _ { 2 } emission is predominantly shock excited , both the expanding ionization front ( classified as subsonic , “ D-type ” ) and the associated shock front farther out ( traced by H _ { 2 } ) can be identified , observationally confirming for the first time a classical scenario that is predicted by evolutionary models of H ii regions .
Integrated line intensity ratios of the observed molecules are determined , implying a mean C ^ { 18 } O/C ^ { 17 } O abundance ratio of 4.13 \pm 0.13 that reflects the ^ { 18 } O/ ^ { 17 } O isotope ratio .
This ratio is consistent with values determined in nearby clouds .
Right at the edge of the void , however , the oxygen isotope ratio might be smaller .