Hydrogen bonding local softness

Hydrogen Bonding The Role of (Local) Softness in (Very) Strong Hydrogen Bonding... 

In Figure 27.3, the relationship between the hydrogen bond energy and the product of the local softness values of donor and acceptor atom (A and B) is given for a series of closely related O—H O types of bonds (NR2, N02 family, etc.). 

FIGURE 27.3 (continued) (c) Combined effect of the local softness values of the acceptor and donor atoms on hydrogen bonding energy. (Reprinted from Ozen, A.S., Aviyente, V., De Proft, F., and Geerlings, P., J. Phys. Chem., A110, 5860, 2006. With permission.)... 

Besides the peaks of the local proton modes typical for hydrogen bond, a sharp peak at 28 meV was observed in KDP [34] and attracted much attention [34,38,39]. This peak exists in DKDP at somewhat higher frequency its intensity decreases in both crystals and its width decreases upon the transition from the FE to the PE phase, without any softening of its frequency [38]. Hence, it is concluded that this mode is connected with the phase transition dynamics, i.e., coupled to the polarization fluctuations. This mode is not the tunneling mode or any local mode of proton or deuteron, but rather some collective optical mode of the lattice that involves substantial proton or deuteron displacement. It has been suggested [38] that this mode corresponds to the mode that has a peak at about 200 cm (25 meV) in Raman scattering and infrared reflectivity spectra, and that it is coupled to the soft mode and usually... 

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