\begin{table}%t1 \caption{\label{TabFIR}Far-infrared line flux ratios to the dereddened 5007~\AA\ line as derived from different theoretical models and observations. (See text for details).} %\centerline {\small \begin{tabular}{llllllll} \hline\hline & $\lambda$,~$\mu$m & \multicolumn{5}{c}{$I/I(5007)$} & $f_{\rm PIR}$ \\ & & I-H & BS-F & BS-DC & SD-200$^*$ & Observed$^{**}$ & SD-200$^*$\\ \hline {}[\ion{O}{iv}] & 25.91 & 0.0051& 5.0 & 0.53 & 8.1 & 0.20 & 0.995 \\ {}[\ion{O}{iii}]& 51.81 & 0.031 & 1.34 & 0.72 & 0.67 & 0.25 & 0.999 \\ {}[\ion{O}{i}] & 63.19 & 1.30 & 170 & 12 & -- & 0.07 & -- \\ {}[\ion{O}{iii}]& 88.36 & 0.028 & 0.22 & 0.11 & 0.55 & 0.10 & 0.999 \\ {}[\ion{O}{i}] & 145.5 & 0.038 & 7.8 & 0.75 & -- & $<$0.0024&-- \\ \hline \end{tabular}} \medskip $^*$ Derived in Sects.~\ref{SecIRSD} and~\ref{SecLineI}; $^{**}$ obtained in Sects.~\ref{SecISO} and~\ref{SecSpitzerO}.\\ {Notes}: the last column lists contribution to the line flux in the SD-200 model arising from the photoionized region~(PIR) before the shock. Derivation of the observed line flux ratio values is described in Sect.~\protect\ref{SecIRObs}. The model-predicted [\ion{O}{i}] lines are sensitive to the pre-shock ion number density in the model, see Sect.~\ref{SecOI}. \end{table}