Dipolar coupling axiality

[AMullen]

Hi, I'm trying to fit the dipolar broadening of a doubly labelled protein seen in the low temperature cw-EPR spectrum at X-band using best-fit parameters from one of the singly labelled components and adding in a 'Sys.ee'. Is there any way of specifying to easyspin that the dipolar coupling should remain axial (and traceless) as it is varied?

Here's what I've used to describe my system (given a rough starting point of 2nm for the electron-electron distance):

Code: Select all

Sys.S = [1/2 1/2];
Sys.g = [2.0071 2.0053 2.0019; 2.0071 2.0053 2.0019];

Sys.Nucs = '14N, 14N';
Sys.n = [1 1];
Sys.A = [7.2 16.0 102.6 7.2 16.0 102.6; 7.2 16.0 102.6 7.2 16.0 102.6];
Sys.lwpp = 0.8;

Sys.ee = [-3 -3 6];

Vary.ee = [3 3 6];

Also, does anyone else use this method for fitting dipolar broadening for low temp cw-EPR at X-band? If so is there anything else I should be aware of when trying to fit this sort of spectrum?

Many thanks,
Anna

[Stefan Stoll]

This is not directly possible with the current version (5.2.5), but I agree it would be very useful to have a way to specify an axial dipolar tensor. Similar capabilities already exist for hyperfine tensors (Sys.A vs. Sys.A_).

You can still do this with the current version by using a custom simulation function, see here.

[AMullen]

Thanks! I'll give that a try. If I get it working I'll post a copy of the script for any others looking at a similar problem.

[Stefan Stoll]

The next EasySpin release after 5.2.x will support this with the field Sys.dip.