Abstract
A first, versatile, computer-controlled temperature-jump NMR apparatus was constructed. The system uses compressed air or nitrogen gas for changing the temperature of the sample solution and maintaining it during data acquisition. The sample is placed in a pyrex capillary tube of 3 mm o.d. on a conventional high-resolution NMR probe. The temperature of the sample is changed by controlling gas flows with three different temperatures, T1, T2, and T3. First, a gas of temperature T1 maintains the sample at its initial temperature. Then a gas of T2 is sent to the probe for 1–2 s for momentary over-cooling or over-heating. And finally a gas of T3 is sent to maintain the final temperature. In this way, either temperature-jump up or down by as much as 20 °C is attained in about 6 s. After the final temperature is reached in the sample, free induction decay signals are acquired at constant time intervals. For a reversible reaction, the entire heat cycle can be repeated under full control by the NMR pulse programmer. Finally, the accumulated free induction decay signals are Fourier transformed to give time-dependent spectral changes (‘‘NMR snap shots’’) occurring in the time range of seconds or longer.
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