Normalized ice absorbance at each equilibrated temperature for ¹²CO ice (red squares) and ¹³CO ice (blue circles) obtained from each of the three TID experiments per isotopologue, showing (A) the entire TID temperature range and (B) the range of temperatures with measurable desorption. Exponential decay fits from Eq. (1) are shown as solid lines. Fit parameters are: A_° = 1.01 ± 0.2, A = (−1.0 ± 4.0) × 10⁻³³, and τ = − 0.38 ± 0.04 K for ¹²CO; and A_° = 1.02 ± 0.02, A = (−0.6 ± 2.0) × 10⁻³⁴, and τ = −0.37 ± 0.02 K for ¹³CO. Both curves have an associated R² > 0.97.