Energy flux, computed as $\nu F_{\nu }^{\text{int }}$, emitted toward the preshock at z = 0 as a function of the wavelength of the emitted photon. The black curve corresponds to the total continuum emission (including Bremsstrahlung, bound-free, and two-photon processes) and the colored spikes to line emissions. Spikes are colored according to the element responsible for the line emission regardless of its ionization state. Predictions are shown for shocks at different velocities, ranging from 10 km s⁻¹ (top left panel) to 400 km s⁻¹ (bottom right panel). All other parameters are set to their standard values (see Table 1). The dashed gray vertical line indicates the ionization threshold of hydrogen.