  Using the 15-m Swedish ESO Sub-millimeter Telescope (SEST), CO, HCN, and HCO+
observations of the galactic star-forming region NGC6334 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 NGC6334--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 ~40--50K in the molecular cloud and >=200K 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 2.2um 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 C18^O/C17^O
abundance ratio of 4.13+-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.
