Impact of peak H density (solid lines (10⁷ cm⁻³) versus dotted lines (10⁶ cm⁻³)) on simulated abundances of selected species during the cloud-collapse phase. Plots on the left and the right are for the ice and gas-phase abundances, respectively. Legends in the top left plot are for both plots at the top, and legends in the bottom left plot are for both plots at the bottom. All solid lines are for model N7-Tg200-Td20, and all dotted lines are for model N6-Tg200-Td20 (see Table 3 for details of each model).