EasySpin forum

Hello All,

I am a new user in Easyspin, recently I got a 51V EPR spectrum within solution phase under Room temperature.
From the spectrum, I think there are more than one components (multiple oxidation states include), and try to figure out how many oxidation states there and the relevant ratio.
After modified a script with two components, the parameters reach 16 (I dont think this is a good start point, also because I even have no experience on Easyspin fitting). So I narrow down to one component try to fit some predominant peaks. however, the 8 parameters still running heavily and didt give good result. so please if anyone has background on 51V multiple components fitting or have good suggestions, very appreciate, please help.
Here the script:
clear, clc, clf

%Load experimental data

[B, spc] =textread('L-VONPs-7.65-20241128.txt', '%f %f', 'headerlines',1);

plot(B, spc);

Sys1.g = [1.98, 1.973, 1.937];
Sys1.A=[104 64 550];
Sys1.Nucs = '51V';

Sys1.lwpp = 1.5; % mT
Sys1.logtcorr =-9.5;
Exp.mwFreq = 9.8; % GHz
Exp.Range = [200.1 500.1]; % mT
Exp.nPoints = 4000;
Sys = {Sys1};

Vary1.g = [0.01, 0.02, 0.01]; % Check if this g-tensor is correct for your system
Vary1.A = [10 10 10]; % Check if hyperfine values are reasonable

Vary1.lwpp = 0.2; % Ensure line width is set correctly

Vary1.logtcorr =1;
Vary = {Vary1}; % Now includes variability for the third system

% Call the fitting function
FitOpt.Method = 'simplex'; % Try a more robust method
SimOpt.Method = 'simplified'; % Switch to simplified method for faster convergence

esfit(spc,@chili,{Sys,Exp,SimOpt},{Vary}, FitOpt);

% Save the fitted spectrum and magnetic field to a file
eprsave('myfile',B,spc,'EasySpin simulation');

I doubt that you are seeing multiple oxidation states. Try fitting with a single component first.

It looks like you are fitting g and A as well as the rotational correlation time. I would suggest to measure a frozen spectrum and fit that to obtain g and A, then keep g and A fixed when you analyze the room-temp solution spectrum.

Hello Stefan,

Thank you so much for your suggestion.
Our instrument can not running sample under frozen phase（just can run the sample under room temperature), that is why I just can run the sample in solution phase after reaction.
From your view, my sample may just have one component? Thank you.

Yanan

I would start the analysis with the assumption of a single species. Maybe focus on fitting the isolated high-field lines first. Here is a starting point, assuming this is a tumbling vanadyl:

clear, clc

VO.S = 1/2;
VO.Nucs = '51V';
VO.A = 263+[-1 -1 2]*105;
VO.g = [1.984 1.984 1.964];

VO.tcorr = 0.1e-9;

Exp.mwFreq = 9.5;

chili(VO,Exp);

This gives 8 lines. Check if your experimental spectrum has these 8. If yes, and you still have additional peaks, you have another species.