Linewidths in the fast-motional regime
lw = fastmotion(Sys,B0,tcorr) [lw,mI] = fastmotion(...)
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. |
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.
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