  We investigate the physical conditions of the gas, atomic and molecular, in
the filaments in the context of Photo-Dissociation Regions (PDRs) using the
KOSMA-PDR mode of clumpy clouds. We also compare the [CII] vs. [NII] integrated
intensity predictions in Abel et al. 2005 for HII regions and adjacent PDRs in
the Galactic disk, and check for their applicability under the extreme physical
conditions present in the GC. Our preliminary results show that observed
integrated intensities are well reproduced by the PDR model. The gas is exposed
to a relatively low Far-UV field between 10^2 - 10^3 Draine fields. The total
volume hydrogen density is well constrained between 10^4 - 10^5 cm^-3. The
hydrogen ionization rate due to cosmic-rays varies between 10^-15 and 4x10^-15
s^-1, with the highest value ~ 10^-14 s^-1 found towards G0.07+0.04. Our
results show that the line-of-sight contribution to the total distance of the
filaments to the Arches Cluster is not negligible. The spatial distribution of
the [CII]/[NII] ratio shows that the integrated intensity ratios are fairly
homogeneously distributed for values below 10 in energy units. Calculations
including variation on the [C/N] abundance ratio show that tight constraints on
this ratio are needed to reproduce the observations.
