3 research outputs found
First principles calculation of inhomogeneous broadening in solid-state cw-EPR spectroscopy
We present a scheme for the first-principles calculation of EPR lineshapes for
continuous-wave-EPR spectroscopy (cw-EPR) of spin centers in complex chemical
environments. We specifically focus on poorly characterized systems, e.g.
powders and frozen glasses with variable microsolvation structures. Our
approach is based on ab initio molecular dynamics simulations and ab initio
calculations of the ensemble of g- and A-tensors along the trajectory. The
method incorporates temperature effects as well as the full anharmonicity of
the intra- and intermolecular degrees of freedom of the system. We apply this
scheme to compute the lineshape of a prototypical spin probe, the
nitrosodisulfonate dianionic radical (Fremy's salt), dissolved in a 50 : 50
mixture of water and methanol. We are able to determine the specific effect of
variations of local solvent composition and microsolvation structure on the
cw-EPR lineshape. Our molecular dynamics reveal a highly anisotropic solvation
structure with distinct spatial preferences for water and methanol around
Fremy's salt that can be traced back to a combination of steric and polar
influences. The overall solvation structure and conformational preferences of
Fremy's salt as found in our MD simulations agree very well with the results
obtained from EPR and orientation-selective ENDOR spectroscopy performed on
the frozen glass. The simulated EPR lineshapes show good agreement with the
experimental spectra. When combined with our MD results, they characterize the
lineshape dependence on local morphological fluctuations