Extremely strong temperature-dependent Davydow-splitting effects in the polarized IR spectra of the hydrogen bond: Pyrazole and quinolin-2(1H)-one crystals

Polarized IR spectra were recorded in the spectral range of the νN–H and νN–D proton stretching vibration bands for the isotopically neat and isotopically diluted crystals of pyrazole (Pzl) and quinolin-2(1H)-one (2HQ). The spectra measured in the temperature range of 77–293 K have shown that temperature extremely strongly influenced the magnitude of the Davydow-splitting effects in the crystalline spectra. Two different competing vibrational Davydow-coupling mechanisms involving hydrogen bonds, i.e., the ‘tail-to-head’ and the ‘side-to-side’, were responsible for the generation of the temperature effects in the polarized spectra.