DMPO-OH g-value variation

[MariaM]

I collected an EPR spectrum of DMPO-OH (produced by photolyzing H2O2 in water with DMPO) to practice fitting in Easyspin. I adapted the code from the fitting example on the YouTube channel and used the literature g-value of 2.0062, allowing for a variation of 0.004. I was satisfied with the fit, but the best fit g-value turned out to be 2.00829. I am confused as to why it is so different from the reported value. Does it have to do with the instrument?

[Stefan Stoll]

It might be that the magnetic field on the instrument is not calibrated accurately enough.

Also keep in mind that g-values can depend on the nanoenvironment of the radical, for example the solvent, and on the state (liquid vs. solid).