Degeneracy analysis for the combination of H₂O (15 K) + H₂O (75 K): 10:90. Panels a–c: stretching, bending, and librational modes of H₂O ice, respectively, at 15, 40, and 75 K. These panels highlight the temperature effect on the band shapes in the water ice IR spectra. Panel d: recurrence pie chart for the fit of the combined data H₂O(15 K):H₂O(75 K) with proportions 10:90 and without adding Gaussian noise to the spectrum. Panel e: same as panel d, but after adding Gaussian noise to the spectrum (σ = 0.01).