Strange lines in the spectrum S=5/2 Sys.D=[2300 ~0] system near zero mT and their dependence on Exp.Range.

[Denis2222224]

Hello everyone. I am trying to calculate the powder EPR spectrum for the Fe3+ ion. During the calculations I came across spectra that have something strange at 0 mT. Please tell me, is this how it should be and am I missing something, or is this some kind of artifact? If it is an artifact, how can I deal with it?

Code: Select all

clc
clear all

Sys.S = 5/2;
Sys.g = 2;
Sys.lwpp = [0 5];
Sys.weight = 1;
lambda = 0.001;
D = 2300;
Sys.D = [D D*lambda];

Exp.Range = [0 600];
Exp.mwFreq = 9.209;
Exp.nPoints = 500;
Opt.Threshold = 0;

figure;

Opt.GridSize = [34 0]; 

I1_left = pepper(Sys, Exp, Opt);

subplot(1, 2, 1); 
hold on;
plot(linspace(Exp.Range(1), Exp.Range(2), length(I1_left)), I1_left, 'b', 'LineWidth', 1.5);


Exp.Range = [5 600];
I2_left = pepper(Sys, Exp, Opt);


offset_left = 0.5 * max(I1_left);
plot(linspace(Exp.Range(1), Exp.Range(2), length(I2_left)), I2_left + offset_left, 'r', 'LineWidth', 1.5);

xlabel('Magnetic Field (mT)');
ylabel('Intensity (offset applied)');
title('GridSize = [34 0]');
legend({'Spectrum I', 'Spectrum I2 (offset)'}, 'Location', 'best');
grid on;
hold off;


Opt.GridSize = [90 0]; 


Exp.Range = [0 600];
I1_right = pepper(Sys, Exp, Opt);


subplot(1, 2, 2); 
hold on;
plot(linspace(Exp.Range(1), Exp.Range(2), length(I1_right)), I1_right, 'b', 'LineWidth', 1.5);


Exp.Range = [15 600];
I2_right = pepper(Sys, Exp, Opt);


offset_right = 0.5 * max(I1_right);
plot(linspace(Exp.Range(1), Exp.Range(2), length(I2_right)), I2_right + offset_right, 'r', 'LineWidth', 1.5);

xlabel('Magnetic Field (mT)');
ylabel('Intensity (offset applied)');
title('GridSize = [90 0]');
legend({'Spectrum I', 'Spectrum I2 (offset)'}, 'Location', 'best');
grid on;
hold off;

sgtitle('Comparison of Spectra with Different GridSize');

Новый точечный рисунок.jpg (185.82 KiB) Viewed 634 times

[Stefan Stoll]

You are encountering a situation where there is a transition at exactly zero field, since you have nu_my = 4*D. The resonance field of transition is orientation-independent and will therefore accumulate significant intensity in a powder average.

Here is the level diagram that illustrates this situation:

Code: Select all

clear, clc

Sys.S = 5/2;
Sys.g = 2;
Sys.D = 2300*[1 0];
levelsplot(Sys,'z',[0 600],9.199)