engleski

Electron nuclear double resonance evidence for bifurcated hydrogen bonds in KH2PO4: Possible role in the ferroelectric transition

Electron nuclear double resonance measurements on O-H...O protons in KH2PO4, using SeO43- as a probe, demonstrate that the superhyperfine tensor for the ''far'' (O...H) proton is dominated by dipolar interaction with the unpaired electron in the 2p(z) orbital of an oxygen to which a ''close'', i.e., O-H, proton is attached. This result implies that each hydrogen is involved in a bifurcated hydrogen bond. This conclusion was supported by a reanalysis of the earlier reported ENDOR data that was obtained using the AsO44- radical as a probe in KH2AsO4, in particular, by the fact the isotropic part of the tensor for the ''far'' protons in sizable (2.8 MHz) and has same sign (negative) as that of the ''close'' proton. Moreover, the various O...H distances and bond angles for the proposed bifurcated hydrogen bonding are comparable to the literature values for these parameters for carbohydrates. These findings provide the basis for a new contribution toward the role of hydrogens in the mechanisms of phase transition in the KDP-type ferroelectrics.

phase-transitions ; paramagnetic-resonance ; spin-resonance ; O-H ; ENDOR ; temperature ; dependence ; dynamics ; distance ; crystals

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