EasySpin forum

Dear EasySpin community,

I'm a relatively new EPR user, and an even newer EasySpin newbie hoping to get some insights with fitting a model to my data.

To describe my system: I am using photocatalytic material to generate hydroxyl and superoxide radicals while running cw-EPR in operando. I'm using BMPO as my spin trap of choice as the more common choice, DMPO, is known to have some issues with superoxide radicals. As a result, I'm expecting the BMPO-OOH adduct signal, as well as some potential BMPO-OH signals.

I have done my best at reviewing literature and the resources (loved the EasySpin Academy 2020 series on Youtube) to get started on fitting my data. Unfortunately I seem to be stuck and would be most grateful for any assistance!

In my attempt, I've defined a total of four components as BMPO-OH and BMPO-OOH each have two diastereomers that each have their own set of hyperfine coupling constants. I am unfortunately unfamiliar with parameters such as the Lorentzian broadening, so I've arbitrarily set values and allow them to vary by 0.05. My approach has been to first simulate a 2-component system with both diastereomers of BMPO-OOH, which I have been able to do to some success with both garlic and chili (chili worked slightly better for me). The fit is far from perfect which is why I believe a 4-component system is more representative. However, when I try to simulate the 4-component system with my previous set of BMPO-OOH parameters fixed, I'm unable to converge to a good solution. I've spent many hours letting the computer run to no avail.

I've attached my MATLAB file, while the data is pasted below as I could not upload the txt file. I've set the non-peak area to zero as the noise was throwing off my previous attempts at fitting the data.

Sincerest thanks in advance for any help that comes my way.

Field [G] Value
3278.9 0
3279 0
3279.1 0
3279.2 0
3279.3 0
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3364.1 0
3364.2 0
3364.3 0
3364.4 0
3364.5 0
3364.6 0
3364.7 0
3364.8 0
3364.9 0
3365 0