Quantitatively, the simulated difference spectra for both the Type IIa conformer and the 1:1 Type Ia-IIa conformer mixture show a narrower broadening compared to the experimental result, with a peak broadening of about 200 cm -1 in our simulations versus about 400 cm -1 in the experiment. Several factors could contribute to this difference. One is that the choice of the electronic functional can affect the peak position as well as the mode couplings. Another factor is that these simulations are performed in the pure gas phase, which neglects the matrix environment that might also couple with the molecular modes and further broaden the spectrum. Both factors will be discussed in more detail in the following paragraphs. Nonetheless, the qualitative similarity in peak broadening and the consistent peak centering near the experimental value of 3025 cm⁻¹ strongly support the conclusion that the Type IIa hydrogen-bonded O-H stretch overlaps with the C-H stretch region.