Thermometers for low temperature Magic Angle Spinning NMR.

The measurement of temperature in a Magic Angle Spinning NMR probe in the temperature range 85-300K is discussed. It is shown that the shift of the (119)Sn resonance of Sm(2)Sn(2)O(7) makes a good thermometer with shift being given by delta=223 - 9.54x10(4)/Tppm and a potential precision of better than 0.5K over the entire temperature range. The sensitivity is such (e.g. 4.2ppm/K at 150K) 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 approximately 1s enabling relatively rapid temperature changes to be followed. Values for the chemical shift of (207)Pb in Pb(NO(3))(2) down to approximately 85K are also presented. Although the (207)Pb shift variation is approximately linear near room temperature (we find a slope 0.725+/-0.002ppm/K over the range 293-153K), it clearly deviates from linearity below approximately 130K.