FIGURE 1.

Diagram defining parameters for the tether-in-a-cone model. The axes X, Y, and Z are the axes of the two nitroxides with X along the N-O bond and Z perpendicular to the plane of the nitroxide and with all subscripts referring to nitroxide 1 or nitroxide 2. The two cones are separated by at their bases and their relative orientation is determined by the angles ψ₁, ζ₂, and ψ₂ (ζ₂ not shown). The orientation of the two cones with respect to the magnetic field, is determined by the angles θ and φ (φ not shown). The orientations of the tethers, and within their respective cones are determined by the angles ν, μ, and λ (ν and λ not shown). The orientation of the tethers with respect to the nitroxide axis systems are determined by the angles α, β, and γ (α and γ not shown). Those angles that are not shown for the sake of simplicity correspond to Euler angle rotations about the appropriate Z axis as defined in Eqs. 2–8.