title: Simulation methods for looping transitions.
abstract: Looping transitions occur in field-swept electron magnetic resonance spectra near avoided crossings and involve a single pair of energy levels that are in resonance at two magnetic field strengths, before and after the avoided crossing. When the distance between the two resonances approaches a linewidth, the usual simulation of the spectra, which results from a linear approximation of the dependence of the transition frequency on magnetic field, breaks down. A cubic approximation to the transition frequency, which can be obtained from the two resonance fields and the field-derivatives of the transition frequencies, along with linear (or better) interpolation of the transition-probability factor, restores accurate simulation. The difference is crucial for accurate line shapes at fixed angles, as in an oriented single crystal, but the difference turns out to be a smaller change in relative intensity for a powder spectrum. Spin-3/2 Cr3+ in ruby and spin-5/2 Fe3+ in transferrin oxalate are treated as examples.
authors.affiliation: National High Magnetic Field Laboratory and Institute for Molecular Biophysics, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida, 32310, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Gaffney
authors.forename: H J
authors.initials: HJ
authors.lastname: Silverstone
mesh_terms: D003198:Computer Simulation; D004574:Electromagnetic Fields; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008962:Models, Theoretical; D011336:Probability; D012984:Software