Dispersion GUI mode - dispersion setup

The next step is to set up the data defining the relaxation dispersion process. This is performed by clicking on the buttons between the “Spin cluster ID” and “Spectra list” GUI elements. The buttons are as follows:

Spin isotope:

This is needed to specify the spin isotope information for each spin in the system, for example if the data is from ¹⁵N, ¹³C, ¹H, etc. The button launches the spin.isotope user function (see section 17.2.226 on page ).

R₁ relaxation data:

This is used to load a text file containing R₁ relaxation data for each spin of interest (see Chapter 5 for calculating R₁ values). The button launches the relax_data.read user function (see section 17.2.155 on page ). It is currently only used for handling off-resonance effects in the R_1ρ-type dispersion data but may be extended, in the future, to handle off-resonance effects in the CPMG-type experiments.

Chemical shift:

As with the R₁ button, this is for properly handling off-resonance effects in the R_1ρ-type dispersion data. The button launches the chemical_shift.read user function (see section 17.2.23 on page ).

Interatomic interaction:

This button launches the interatom.define user function (see section 17.2.58 on page ). This is needed to link, for example, ¹H to ¹⁵N spins into a spin system so that MMQ-type data, which relies on a multiple-spin system, can be handled.

Value setting:

When one of the parameters of the dispersion model is already known, its value can be set by clicking on this button which launches the value.set user function (see section 17.2.268 on page ). Setting a parameter value will fix the parameter in the initial grid search. However it will be free to vary in the non-linear least squares optimisation used to refine its value.

For SQ CPMG-type dispersion data, only the spin isotope information is required:

In this case, all spins are ¹⁵N. However as no spins are named yet, the text “@N*” cannot be used. So simply change this to “@*” and click on “OK”. The other buttons can be ignored.