Relaxation Delay and Repetition Times

Almost all of the experiments described in this chapter, and certainly all 2D experiments, require some time between scans during which the spin systems that have been irradiated or otherwise perturbed can return to equilibrium. There are two times during which relaxation processes occur (i) the relaxation delay time (DT), which is the period between the end of the acquisition of the signal (ta) and the first pulse of the pulse sequence being used and (ii) the repetition time (RT), which is the sum of DT + tg- Since relaxation occurs during as well as DT, especially for H-detected pulse sequences, it is important to consider RT, and not just DT, when deciding on experimental delay times between pulses. If, for example, it is determined that RT ought to be about 1 s and tg 200 ms, then DT should be set to approximately 800 ms. 

For the heteronucleus-detected FLOCK experiment, longer RT s are appropriate since the signals of nonprotonated nuclei are being recorded. 

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