Orientation/field-dependent line widths

[thanasis]

I am trying to simulate spectra such as reported by Eaton & Eaton here.

The main idea is that Tm times are orientation-dependent, hence in frozen-solution spectra they are effectively field-dependent. To the extent that line widths are Tm-determined, the net effect is that they will be different at different field-positions of the spectra.

In the case of V(IV) (S = 1/2, I = 7/2) which has a small g-anisotropy and the spectra are rather symmetrically distributed around a central resonance, it is not so much the tensor orientation, but the distance from the centre of the spectrum that determines the line widths: resonances along the same direction are narrower or broader depending on where they lie on the spectrum. Consequently, modelling with AStrain/gStrain/gAStrainCorr does not work.

I was wondering whether there might be a way to deal with this and impose an empirical linewidth = f(H) function.

One thought is to define a vector of length equal to that of the spectrum, vary it between 0 and 1 at the appropriate positions and modify the spectral amplitudes.

This is quite brute-force and rather bulky (and doesn't tackle the underlying issue of linewidth). Would there be a smarter way to achieve such a simulation?

Thanks!

[Stefan Stoll]

Interesting. Not sure about the best way to accommodate this in EasySpin. Can you post the spectrum and a rough sim here?

[thanasis]

Here are the spectra files and a fitting script.

[thanasis]

You may see that the flat parts of the simulations do not follow the parts where Tm has drop-offs.

[Stefan Stoll]

Hmm, pepper does not have an orientation-dependent Lorentzian broadening.

You could use resfields to calculate resonance positions and amplitudes for a set of orientations, then multiply the amplitudes by a orientation-dependent Tm factor, and then generate the spectrum by accumulating Gaussians into a spectral vector.

Alternatively, and probably better, you could use Exp.Ordering to supply an orientation-dependent amplitude function. Once fitted, you'll then have to analyze the result in terms of Tm.