H-BONDS IN ACETIC-ACID CRYSTALS - INFLUENCE OF TEMPERATURE AND OF ISOTOPIC DILUTION ON O-H(O-D) STRETCHING BANDS

We describe the evolution of the νs bands of CH3COOH, CD3COOH, CH3COOD and CD3COOD crystals when varying temperature from 10 K to 270 K, and also under isotopic dilutions. We discuss the results obtained and we show how we can estimate from these experiments the values of the anharmonic constant coupling νs with νσ (parameter b) and also how we can evaluate the energy of resonance interactions of νs with other modes. The origin of the shift of the centre of gravity of the νs, bands with temperature is discussed and we give arguments against an anharmonic one-dimesional potential for the νσ mode being at the origin of such a shift in acetic acid crystals. We suggest that this shift might rather be due to a modulation of νs or νσ by lower frequency modes of the H-band. In the conclusion we summarize our results on acetic acid crystals and stress the interest of performing such quantitative studies. © 1979.