Nuclear quadrupole double resonance of 39K in some potassium salts

Abstract

³⁹ K quadrupole resonance signals have been detected in a number of potassium salts at room temperature by the method of double resonance using adiabatic demagnetization. In some of the compounds, such as potassium bicarbonate and bisulphate, the lines under suitable experimental conditions are doublets with splittings of 30.5 and 22 kHz, respectively. It is shown by theoretical and experimental analysis that these signals arise from the “solid effect”, with some contribution from thermal mixing; the splitting of the doublets is directly related to the inverse cube of the interproton distance within the (HCO₃)^2–₂ and (HSO₄)^2–₂ dimers in these two crystals. A point-charge calculation is used with some degree of success to derive the orientation and sign of the ³⁹K electric field gradient tensors. In KHCO₃, ⁴¹K quadrupole has also been detected and a weak doublet observed in KHSO₄ near 2.355 MHz is tentatively assigned to ³³S.