H-BONDS OF ADIPIC ACID CRYSTALS AT LOW-TEMPERATURE .1. EXPERIMENTAL RESULTS FROM POLARIZED IR SPECTROSCOPY

Polarized IR studies at low temperature on H and Dadipic acids lead to several interesting results. First, the νCO modes have a well defined polarization at 10 K but have several polarizations at higher temperatures. This result can be attributed to the existence of two isomers for the (COOH)2 dimeric cycles, with one isomer having an energy which is about 1.5 kcal/ mole higher than that of the other. Then two other results, directly relevant to H-bonds have been found: the polarization of the νs band (O H→ O or 0 D→ 0 ) is not constant but varies by about 15° between its low- and high-frequency side; the 2γOH and 2γOD overtone bands have polarizations which are nearly the same as that of the νs bands. thus strongly suggesting that they borrow their intensities from the νs bands. These results are theoretically discussed in the paper which follows this one. © 1979.