CommunicationThermometers for low temperature Magic Angle Spinning NMR

The measurement of temperature in a Magic Angle Spinning NMR probe in the temperature range 85-300 K is discussed. It is shown that the shift of the 119Sn resonance of Sm2Sn2O7 makes a good thermometer with shift being given by δ = 223 - 9.54 × 104/T ppm and a potential precision of better than 0.5 K over the entire temperature range. The sensitivity is such (e.g. 4.2 ppm/K at 150 K) that small temperature gradients across the sample can readily be measured. Furthermore, since the spin-lattice relaxation time is very short, measurements can be made in ∼1 s enabling relatively rapid temperature changes to be followed. Values for the chemical shift of 207Pb in Pb(NO3)2 down to ∼85 K are also presented. Although the 207Pb shift variation is approximately linear near room temperature (we find a slope 0.725 ± 0.002 ppm/K over the range 293-153 K), it clearly deviates from linearity below ∼130 K.