Theoretical [Cl II] line intensity ratio ﹩R_{1}=I( 3s^{2}3p^{4}﹩ ¹D₂–﹩3s^{2}3p^{4}﹩ ¹S₀)﹩/I( 3s^{2}3p^{43}P_{2}﹩–﹩3s^{2}3p^{4}﹩ ¹D₂) ﹩=I﹩(6161.8 Å)﹩/I﹩(8578.7 Å), where I is in energy units plotted as a function of logarithmic electron density (﹩N_{e}﹩ in cm⁻³) at an electron temperature of ﹩T_{e}=10^{4.1}﹩ K. Solid line: Calculations with the electron impact excitation rates of Wilson & Bell (2002). Dashed line: Calculations with the atomic data of Krueger & Czyzak (1970).