For an O–H mixture, ƒ_On/Hn=1/2 is the fraction of the photoelectron energy, E₀, that goes into various inelastic channels specified by their initial and end levels. Then, H^* and O^* refer to the summation over all excited levels within the corresponding neutral atoms. For each panel, the four curves that are displayed (distinguishable by their thickness) refer to fractional ionizations log₁₀(x_e)=−1 (thickest), −2, −3, and −4 (thinnest). Calculations done with the LG90 set of cross sections.