Question about logtcorr

[AlexMorley]

I'm having issues with the esfit('chili') command on EasySpin, specifically the logtcorr parameter.
Do the three values correspond to [τz τy τx] in that order?
Or can they be rearranged as τz > τy > τx, as when simulated they are called logtcorr(1), logtcorr(2) and logtcorr(3).

As I understand it the rotational correlation time (tcorr, τ) corresponds to the time taken to rotate one radian around a principle axis (x, z or y). Due to the definition of the principle axes of a spin label, τz > τy > τx, the z-axis is parallel with the nitroxide p-orbitals, the x-axis is parallel to the nitroxide bond and the y-axis is perpendicular to both. Would I be wrong in this?

Cheers for any help.

[Stefan Stoll]

It does not matter how you order and label the principal axes. The only requirement is that the ordering must be the same for the g- and A-values and the diffusion tensor (and any other collinear tensor). The two following inputs result in identical spectra:

Code: Select all

Sys.g = [gx gy gz];
Sys.A = [Ax Ay Az];
Sys.logtcorr = log10([taux tauy tauz]);

Code: Select all

Sys.g = [gz gx gy];
Sys.A = [Az Ax Ay];
Sys.logtcorr = log10([tauz taux tauy]);