1H ENDOR investigations on gamma-irradiated betaine calcium chloride dihydrate in the incommensurate phase

The electron nuclear double resonance (ENDOR) technique is applied to study the influence of the incommensurate modulation on the proton hyperfine structure (hfs) tensors of the N(CH₃)₃ radical in betaine calcium chloride dihydrate (BCCD). The temperature dependence of the edge singularities due to the increasing of the incommensurate (IC) modulation amplitude could be observed in the¹H ENDOR of the CH₃ groups for the first time. The rotation pattern of the edge singularities observed in the¹H spectra in the IC phase of BCCD can be explained by a libration around the C₁-N axis with a tilt angle of about ±7°.