Fluxes of Lyα (left) and Lyβ (right) in precursor (top) and postshock positions (bottom). The positions of the cuts – labelled PRE (red), PEAK (blue) and DEEP (green) – are shown in Fig. 5 by the vertical dashed lines, and the black lines give the fluxes at the shock front z = 0. Vertical greylines show line centres of Lyα and Lyβ (solid), H₂ Lyman (dashed) and Werner (dotted) band absorption lines, with an emphasised v = 6 − 0 P(1) H₂ line (thick dashed). The precursor vertical lines are Doppler-shifted by the shock velocity, whereas in the postshock panels they are shifted by flow velocity at the peak of the emission, V_z ~ 4 km s⁻¹ for Lyα and V_z ~ 7 km s⁻¹ for Lyβ. The arrows between the top and bottom panels highlights the velocity shift between the preshock gas and at peak emission. We note that none of the y-axes scales are the same.