why the simulated spectra are different between the mixture isotopes of Cl and the single enriched 35Cl or 37Cl

[weitong]

Hello,

I got a simulation which I cannot understand.
I try to simulate a 1/2 freeradical with Cl atom. With the natural abundance of mixture of Cl isotopes, it gives the spectrum(green line):

With the enriched 35Cl or 37Cl isotope, both of them gives the same spectra (red-35Cl, blue-37Cl):

The question is, both of the 35Cl and 37Cl isotopes have the same spectrum, but the mixture shows differrent structures, why?
All the g and A parameters are the same.

Code: Select all

%======================================
clear %, clf

% component 1: Radical =====
Sys1.S = 1/2;
Sys1.g = [2.00600 2.00600 2.00600];
Sys1.lwpp = [0.000/10 3.219/10];
Sys1.weight =  1.00;
Sys1.Nucs = 'Cl';
Sys1.n = [1];
A_Gauss1 = [20.04 20.04 20.04];
A_MHz1 = mt2mhz(A_Gauss1/10,gfree);
Sys1.A = A_MHz1;
% component 2: Radical1 =====
Sys2.S = 1/2;
Sys2.g = [2.00600 2.00600 2.00600];
Sys2.lwpp = [0.000/10 3.219/10];
Sys2.weight =  1.00;
Sys2.Nucs = '35Cl';
Sys2.n = [1];
A_Gauss2 = [20.04 20.04 20.04];
A_MHz2 = mt2mhz(A_Gauss2/10,gfree);
Sys2.A = A_MHz2;
% component 3: Radical3 =====
Sys3.S = 1/2;
Sys3.g = [2.00600 2.00600 2.00600];
Sys3.lwpp = [0.000/10 3.219/10];
Sys3.weight =  1.00;
Sys3.Nucs = '37Cl';
Sys3.n = [1];
A_Gauss3 = [20.04 20.04 20.04];
A_MHz3 = mt2mhz(A_Gauss3/10,gfree);
Sys3.A = A_MHz3;
Exp.mwFreq = 9.399247;
Exp.Range = 335.000000+ [-1 1]*5.000000;
Exp.nPoints = 2000;
comp1 = garlic(Sys1, Exp);
comp2 = garlic(Sys2, Exp);
comp3 = garlic(Sys3, Exp);
comps = [comp1;comp2;comp3];
[Field,spc] = garlic({Sys1,Sys2,Sys3},Exp);

Thanks,
WT

[Matt Krzyaniak]

When using specific isotopes, the provided hyperfine values directly determine the splitting, however when using the natural isotope abundance, the input hyperfine value gets scaled by the nuclear g-value difference. So in your case the lower abundance 37Cl should use a set of hyperfine values scaled by 0.456/0.5479 = 0.83.

[Stefan Stoll]

Matt is right.

For completeness: You can get the isotope table by typing isotopes, and you can get the nuclear g values with nucgval('35Cl') etc.

[weitong]

I see. Thanks.