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 v(N-H) and v(N-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. (C) 2014 Elsevier B. V. All rights reserved.