The relaxation values of the set R'(θ) include the spin-lattice, spin-spin, and cross-relaxation rates at all field strengths. These rates are respectively (Abragam, 1961)
where J(ω) is the power spectral density function and Rex is the relaxation due to chemical exchange. The dipolar and CSA constants are defined in SI units as
where μ0 is the permeability of free space, γH and γX are the gyromagnetic ratios of the H and X spins respectively, is Plank's constant divided by 2π, r is the bond length, and Δσ is the chemical shift anisotropy measured in ppm. The cross-relaxation rate σNOE is related to the steady state NOE by the equation
The relax user manual (PDF), created 2019-06-14.