Grain-size-dependent mass extinction coefficients (solid lines) and absorption coefficients (dashed line) for model compositions corresponding to model sets A, B, C, D, E, F, and G, from the upper left to the lower right, respectively. The mass extinction coefficients for increasing effective grain radius a_eff are shown. See text for details. For each set, a close-up of the CO₂ stretching mode is shown below it (for the last two panels, this also includes CO).