Effects of 'excessive' exciton interactions in polarized IR spectra of the hydrogen bond in 2-butynoic acid crystals: Proton transfer induced by dynamical co-operative interactions involving hydrogen bonds

In this article, we present the results of our study of polarized IR spectra of the hydrogen bond in crystals of 2-butynoic acid (CH3C≡CCOOH) as well as in crystals of its deuterium derivative (CH3C≡CCOOD). 2-Butynoic acid can exist in two polymorphous crystalline forms: in the 'α' form, based on a classic dimer motif and in the 'β' form, based on the catamer pattern of the hydrogen bond arrangement. By cooling the melted substance crystals of the 'β' phase were obtained selectively. The polarized IR spectra of the hydrogen bond in the 'β' form of 2-butynoic acid crystals were measured at room temperature and at the temperature of liquid nitrogen in the νO-H and νO-D band frequency ranges. In terms of the 'strong-coupling' theory the fine structure patterns of the νO-H and νO-D polarized bands were quantitatively explained along with the dichroic and the H/D isotopic effects in the spectra. To interpret the main properties of the spectra the existence of a non-conventional effect concerning a self-stimulated concerted proton position rearrangements in the neighboring cells in the lattice had to be assumed. On the basis of the spectra of isotopically diluted crystalline samples of 2-butynoic acid it was suggested that a random distribution of protons and deuterons occurred in the open chains of the hydrogen bonded molecules. However, coordination in the mutual arrangement of protons and deuterons in the neighboring hydrogen bonds from the closely spaced molecular chains was found to be non-random. This fact was ascribed to dynamical co-operative interactions, most strongly involving hydrogen bonds from different chains in the modified lattice. These non-conventional interactions were responsible for appearance of the so-called H/D 'self-organization' isotopic effects in the spectra