Q-branch profiles of different models shown at JWST-MIRI resolving power. All fluxes are normalized to the maximum of the feature. In panel a) LTE point models with a temperature of 200K (cyan), 400 K (red) and 800 K (blue) are shown. Panel b) shows DALI disk models with a constant abundance profile for which the product of abundance times gas-to-dust ratio is constant. All these models have very similar total fluxes. The models shown are g/d_gas = 100, x_CO2 = 3 × 10^-7 in red; g/d_gas = 1000, x_CO2 = 3 × 10^-8 in blue and g/d_gas = 10000, x_CO2 = 3 × 10^-9 in cyan. The spectra are virtually indistinguishable. Panel c) shows DALI disk models with a jump abundance profile, a g/d_dust = 1000, an outer CO₂ abundance of 3 × 10^-8 and an inner abundance of 3 × 10^-7 (red), 3 × 10^-8 (blue), 3 × 10^-9 (cyan). The model with the highest inner abundance shows a profile that is slightly broader than those of the other two. Panel d) shows DALI disk models with the same, constant abundance of x_CO2 = 3 × 10^-8, but with different g/d_dust ratios. Removing dust from the upper layers of the disk preferentially boosts the high J lines in the tail of the feature as emission from the dense and hot inner regions of the disk is less occulted by dust.