Collisional transfer rates, D^k ( j → j′, T), for C₂ rotational levels within the electronic states a ³Π_u. The upper panel shows variation with j of the rates for k = 0 (open diamonds), k = 1 (open triangle), and k = 2 (open circles), where we have set j′ – j = 2 and T = 6000 K. The solid curves show the GP fit values obtained using Equation (10) and GP coefficients of Table A.6. The lower panel displays the variation in the rates with ( j′ - j) for k = 0 (open diamonds), k = 1 (open triangle), and k = 2 (open circles), where we set T = 6000 K, N_j = 13₁₃, and j′ = N′.