A free evolution period is a period in which transverse magnetization  is allowed to freely evolve under the effect of coupling constants and chemical shifts. Thus, pulses are not applied on the selected nuclei.

An example should be the variable evolution period (t₁) of any homonuclear 2D experiments as, for instance, COSY, TOCSY, NOESY or ROESY experiments. After Fourier transform, both chemical shifts and coupling constants of the evolving spins will be displayed in the F₁ dimension of the resulting 2D map:
REQUIREMENTS

Easy implementation on AVANCE spectrometers.

EXPERIMENTAL DETAILS

There are 32 duration parameters, d0-d31,  to be specified in seconds. They are executed as delays without any further actions by the pulse program commands d0. They can be incremented or decremented using the pulse program commands id0-id31 or dd0-dd31, respectively. The changes are given by the parameters IN0-IN31. The pulse program commands rd0-rd31 reset a respective delay to its original value. The delays may also be changed by means of arithmetic expressions during pulse program execution.

 SYNTAX

The standard way to implement a variable evolution delay in a pulse program is:

... d0 ... id0

in which d0 is the variable evolution delay (in seconds) and in0 is the value to be incremented each time id0 is found. In 3D experiments, d10 is used to define the second variable evolution delay similarly as described for d0.

RELATED TOPICS

 Also see: fixed free-evolution delay.