50 \[e\]
  $\rm{[}$O [iii]{}$\rm{]}$     88.36      18.0       5.4    35.12    163                   5 $\times \rm{10^{2}}$ \[e\]
  $\rm{[}$O [i]{}$\rm{]}$       63.18       6.7       2.0      -      228                   5 $\times \rm{10^{5}}$ \[H\]
  $\rm{[}$O [i]{}$\rm{]}$       145.52     0.56      0.17      -      99                    1 $\times \rm{10^{5}}$ \[H\]
  $\rm{[}$N [iii]{}$\rm{]}$     57.32      2.50      0.78    29.60    251                   3 $\times \rm{10^{3}}$ \[e\]
  $\rm{[}$N [ii]{}$\rm{]}$      121.9      0.31      0.10    14.53    118                   3 $\times \rm{10^{2}}$ \[e\]
  $\rm{[}$N [ii]{}$\rm{]}$      205.18   $<$ 0.29      -       ”      70                              45 \[e\]
  ---------------------------- -------- ----------- ------- ------- ------- ------------------------------------------------------------

The [*ISO*]{}/LWS fluxes can be found in [@bergvall-2000], [@brauher-2008], and [@vasta-2010].\
${(a)}$ Upper limits are given as the 3-$\sigma$ uncertainty from the line fit.\
${(b)}$ Excitation potential. Energy to create an ion. For H$\rm{_2}$, it is the energy to photodissociate the molecule.\
${(c)}$ Excitation temperature. Temperature T=$\Delta$E/k required to populate the transition level.\
${(d)}$ Critical density n$_{crit}$ noted \[H\] for collisions with hydrogen atoms (T=100 K and T=300 K for the H$\rm{_2}$ lines), \[e\] with electrons (T=10 000 K). Values are from [@malhotra-2001], [@giveon-2002], and [@kaufman-2006]. \[table:lines\]

Spectral line description
-------------------------

The IRS and PACS spectra probe the ionised and neutral media. The IRS spectrum shows a wealth of MIR fine-structure lines, the brightest being (in order) \[Ne [iii]{}\] 15.6 $\mu$m, \[Si [ii]{}\] 34.8 $\mu$m, \[S 