Polarized infrared spectra of hydrogen-bonded systems by the stretched-polymer method. 2. Transition moment directions of the vibrations of normal and deuterated acetic acid dimers

Abstract

Transition moment directions of the vibrations of dimers of CH/sub 3/COOH, CH/sub 3/COOD, CD/sub 3/COOH, and CD/sub 3/COOD have been measured by using the stretched-polymer orientation method. O-H, C-O, and C=O stretching vibrations are directed almost parallel to the respective bonds. The OCO bending is observed to be directed above 30/sup 0/ from the long axis of the dimers. The rocking OCO vibration is directed almost parallel to the long axis of the dimers in each species. The OH (OD) bending is the only vibration which shows noticeable differences in the directions of transition moments between different isotopic forms. The obtained results are compared to theoretical directions for carboxylic ring in-plane vibrations calculated by the fixed partial charge model using the formic acid dimer as a model system.