Top panel: chemical composition of a simulated pancake (L = 32 Mpc) including cooling and heating without thermal conduction (solid lines) and with thermal conduction (dashed lines). The colors indicate different species (lines from top to bottom): red: H ii, cyan: He ii, magenta: He ii, green: H i, blue: He i; Bottom Panel: chemical composition in the region of the shock (indicated by the box in the top panel) using non-IE chemistry for H i (left) and He ii (right). The corresponding profiles from the top panel are shown in gray for comparison. [See the electronic edition of the Journal for a color version of this figure.]