Why does the IR Spectra of Hydroxide Stretching Vibration weaken with increase in hydration? | Kaito Takahashi

Why does the IR Spectra of Hydroxide Stretching Vibration weaken with increase in hydration?

Citation:: Morita, M, Hirokazu Takahashi, Satoshi Yabushita, Takahashi K. 2014. Why does the IR Spectra of Hydroxide Stretching Vibration weaken with increase in hydration? Physical Chemistry Chemical Physics. 16:23143-23149.