Shifted peaks in EDNMR spectra ?

[Maria]

Hi!

I am trying to simulate EDNMR spectra of 55Mn that interact with S=3 and D~-0.3 cm^-1. There are shifts between the simulated and the experimental spectra about 4-7 MHz. I have tried to decrease the Excitation window, add quadrapole, rotate the AFrame.. Nothing worked.. What else could I try?

[Stefan Stoll]

Have you adjusted the hyperfine values? Post a minimal but working script that shows what you are asking about.

[Maria]

sim.png (21.17 KiB) Viewed 3364 times

The problem is these shifts from the experimental that are marked with red.



Sys.S = 3;
Sys.g = 1.99;
Sys.D = -3e4*[0.281 0.0461];
Sys.aF = [20 -40];

Sys.Nucs='55Mn';
Opt.nKnots=[20 3];
Opt.Method = 'matrix';
Opt.Threshold=1e-4;


Par=struct('ExciteWidth',100,'nPoints',1024,'Harmonic',0,'Temperature',4.8);
Par.mwFreq=94.017;
Par.Range=[0 300];

A=[-95 -97 -91;-102 -103 -97];
lw=[5;5]; scal=[ 0.5 0.5];


for n=1:2;
Par.Field = 1980;
Sys.A=A(n,:)
Sys.lwEndor=lw(n,:);
[x198,MnSim198] = salt(Sys,Par,Opt); MnSim198=MnSim198/max(MnSim198);
LOR= gaussian(x198,0,300);LOR=LOR/max(LOR);
MnSimA198(:,n)=scal(n)*LOR.*MnSim198;
plot(x198,MnSimA198(:,n)-0.1); hold on
end


I cannot add the experimental file.. Thank you!

[Stefan Stoll]

You are simulating an ENDOR spectrum and comparing it to an EDNMR spectrum. The simulation is likely off in the orientation selection and the line intensities.

[Maria]

sim2.png (11.16 KiB) Viewed 3354 times

This is with ExciteWidth=1 and nKnots=[180 6], but it is still the same..

There is a small term missing from the hamiltonian i am using.
For example, for the smaller hyperfine. The experimental peaks are 162MHz and 256 MHz.
It should be: 2A-ω=162 and 3A-ω=256 and 256-162=A
ω~21MHz

The A calculated from each equation is slightly different: 91.5 92.5 94

[Stefan Stoll]

You might be seeing crossterms between zero-field splitting and hyperfine coupling.

[Maria]

what does this mean? I don't understand..

[Stefan Stoll]

The presence of significant zero-field splitting (S>=1) will affect the quantization axis of the electron spin, which in turn affects the nuclear resonance frequencies via the hyperfine coupling. As a result, the nuclear peaks are slightly shifted compared to the case S=1/2.

[Maria]

But, this isn't calculated by easyspin already?

Untitled.png (18.24 KiB) Viewed 3320 times

I corrected a bit the intensities.. for the peak positions I can't do anything..