The effect of strong coupling between vibrations in hydrogen bonds on the polarized spectra of the mercaptobenzothiazole crystal: an “anomalous” isotopic effect

Effects of strong inter-hydrogen bond dynamical couplings in the polarized IR spectra of adipic acid crystals

“…1 and 2). It was shown that the above presented qualitative interpretation of the h 10 and d 2 adipic acid crystal spectra is in general agreement with the model calculations of the ''residual" m O-H and m O-D band contour shapes, performed in terms of the ''strong-coupling" [7,45] or the ''relaxation" theory [26], for centrosymmetric hydrogen bond pairs (dimers) of the ''side-to-side"-type arrangement of moieties. The details of these calculations have already been described previously [26,33,34].…”

“…On the other hand, the higher-frequency branch of each considered band corresponds to the symmetry-allowed transition ascribed to the non-totally symmetric proton or deuteron stretching vibrations in the dimers. It can be satisfactorily reproduced quantitatively by the so-called ''plus" band [7,45] contributing with the F + statistical weight. In this case both component transitions contributing at the generation of each analyzed band should exhibit identical polarization properties [18].…”

“…pole-forbidden transition occurring to the excited state of the totally symmetric proton or deuteron stretching vibrations in the centrosymmetric dimers. This part of each spectrum was satisfactorily reproduced by the so-called ''minus" band from the ''strongcoupling" theory [7,45]. The forbidden transition in the IR may, however, become spectrally activated via the vibronic promotion mechanism, which is a reverse of the familiar Herzberg-Teller mechanism [18] from the electronic spectroscopy of aromatic hydrocarbon molecules.…”

“…The results of similar calculations aiming at the quantitative reconstitution of the corresponding spectra of the d 8 and d 10 adipic acid crystals in terms of the ''strong-coupling" [7,45] theory are shown in Figs. 8 and 9.…”

“…Within the ''strong-coupling" theory, the m O-H band shape for a model dimer, composed of two O-HÁ Á ÁO hydrogen bonds, depends basically on the following system of coupling parameters: (i) on the distortion parameter ''b H ", and (ii) on the resonance interaction parameters ''C O " and ''C 1 [7,45]. The ''b H " parameter describes the change in the equilibrium geometry for the low-energy hydrogen bond stretching vibrations, accompanied by the excitation of the high-frequency proton stretching vibrations m O-H .…”