Molecular opacity cross sections for various species. The top panel shows cross sections for molecules important in cold brown dwarf atmospheres (T = 225 K, P = 1 bar). Cross sections are scaled by the abundance in chemical equilibrium, assuming D/H = 2 × 10⁻⁵. The bottom panel shows the cross section of H₂O at P = 1 bar and temperatures from 200 to 2400 K. Colder temperatures lead to larger amplitudes in molecular opacity.