Chemical and excitation profiles of neutral carbon across the standard model. Top panel: relative abundance of neutral carbon as a function of the distance (bottom axis) or time (top axis) in the shock. The curve is colour-coded according to the value of the thermal pressure along the trajectory. Bottom panel: populations of the three fine structure levels of C as a function of the distance (bottom axis) or time (top axis) in the shock. The vertical grey line in both panels indicates the distance and time at which the gas reaches a fraction, χ = 0.95, of the final density, $n_{\mathrm{H}}^{\mathrm{f}}$.