Phase plots (T _gas vs. total H nucleus, n _H, number density) weighted with L _CII for snapshots at t = 40, 70, 120, 170, 250, and 390 Myr. Before the second encounter (top row), L _CII originates from the WNM (see Figure 4). Once the second encounter occurs (bottom row), H II regions form and their ionized gas takes over as the main contributor to the total L _CII. The horizontal straight line at ﹩\mathrm{log}{T}_{\mathrm{gas}}=4﹩ is the gas temperature of the interior of H II regions.