Infrared Spectral Hole-Burning and Spectral Diffusion of Vibrational N-D Bands in a Disordered Tutton Salt

We have studied infrared spectral hole burning of the N-D stretching bands of NH₃D⁺ in salt (NH₄)₂Co_0.25Ni_0.75(H₂O)₆(SO₄)₂ was at 10 K. It was observed that the spectral line broadening occurred on a logarithmic time scale, which is consistent with the theoretical prediction of standard two-level-system. The temperature of 10 K is also beyond the temperature limit in previous studies on spectral diffusion.