Line Diagnostics {#diagnostics}
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Self-Consistent Shock Modelling
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To analyse the spectrophotometry we have built a family of radiative shocks with self-consistent pre-ionisation using the MAPPINGS 5.12 code, following the methodology described in @Sutherland17, and applied to the study of Herbig-Haro objects by @Dopita17b. The pre-shock density is set by the ram pressure of the shock, taken to be independent of shock velocity; $P_{\mathrm{ram}} = 1.5\times 10^{-7}$dynes cm$^{-2}$, to ensure that the measured \[\] densities (which give the electron density near the recombination zone of the shock) approximately match those produced by the models. For each abundance set, a set of models was run for $100 \leqslant v_s \leqslant 475$km/s in steps of 25km/s. The magnetic field pressure in the un-shocked cloud ahead of the photo-ionised precursor is assumed to be in equipartition with the gas pressure, $P_{\mathrm{mag}} = P_{\mathrm{gas}}$, and the temperature of the gas entering the shock is given by the self-consistent pre-ionisation computation; see @Sutherland17 for details.

The abundance set was initially taken as being 0.5 times the Local Galactic Concordance (LGC) values [@Nicholls17], but was then iterated manually to achieve a better fit of theory to the spectra of the clouds on the standard @BPT81 and 