fastmotion
Introduced in 2.5
Synopsis

Linewidths in the fast-motional regime 

lw = fastmotion(Sys,B0,tcorr)
[lw,mI] = fastmotion(...)
Description

Given the g and A tensors in Sys, the magnetic field (mT) in B0 and a rotation correlation time (seconds) in tcorr, fastmotion computes the widths of the lines broadened by the anisotropies of g and A. The widths are returned in lw, and the associated lines are identified by sets of mI numbers in mI. One row corresponds to one EPR resonance line.

The three input parameters are

Sys Spin system structure containing the list of nuclei Nucs, the g and A tensors g and A, and, optionally, the tensor orientations in gpa and Apa.
For a description these fields, see garlic.
B0 External magnetic field, in mT.
To compute line widhts for a field-swept EPR spectrum, take the center field, as long as the spectrum is not too wide.
tcorr Rotational correlation time for isotropic Brownian rotational diffusion, in seconds.
The correlation time tcorr and the diffusion rate D are related by tcorr = 1/(6*D).

The two output parameters are

lw All line widths (FWHM for Lorentzians), in mT.
mI The mI values for the lines, one line per row.
Algorithm

fastmotion uses the Kivelson formula to compute line widths. Outside the fast-motion regime (= Redfield limit), the formulas are not valid.

The formulas can be found in Neil Atherton's book.

Example

The X-band spectrum of a nitroxide radical in the fast motional regime features three lines with different widths. The widths and the mI values for the associated lines are 

Nitroxide = struct('g',[2.0088 2.0064 2.0027],'Nucs','14N');
Nitroxide.A = mt2mhz([7.59 5.95 31.76]/10);

Field = 350;
tcorr = 1e-10;
[lw,mI] = fastmotion(Nitroxide,Field,tcorr)

lw =
    0.0070
    0.0029
    0.0027
mI =
    -1
     0
     1
See also

garlic