Recently, using the adiabatically switched semiclassical initial value representation (AS-SCIVR), a new assignment was proposed, suggesting that the Type IIa hydrogen bonded O-H stretch is at 3329 cm -1 , near the previously assigned N-H stretching region and significantly outside the C-H stretching region. However, this new peak assignment is also not fully convincing, as the experimental spectra show only a weak and broad N-H stretch signal in the 3300-3400 cm -1 region, This framework has been shown to be remarkably successful for hydrogen-related vibrations. Herein, our study will provide strong evidence supporting the original assignment of the Type IIa hydrogen bonded O-H stretch as appearing within the C-H stretching region as a result of the interplay between electronic effects, NQEs, and matrix effects. The hydrogen bonded O-H vibrational frequencies for the Type IIa proline conformer are provided in Table . The disputed experimental result is 3025 cm -1 , which is the maximum position of a wide and relatively faint peak in the difference spectrum of proline-D0 and proline-D2. Without NQEs, unscaled DFT/B3LYP harmonic analysis predicts the frequency to be 3359 cm , which is about 300 cm - 1 higher than the experimental assignment. When the empirical scale factor of 0.92 as used by Adamowicz and co-workers is applied, the frequency drops sharply to 3090 cm -1 . However, the reliability of empirical scale factors can be questionable, as they often need to vary with vibrational modes as well as electronic structure methods. With AS-SCIVR, this hydrogen bonded O-H vibrational frequency was reported to be 3329 cm -1 , which is similar to the unscaled DFT harmonic result and does not support the experimental assignments.