The IT99 2-site CPMG model

This is the model for 2-site exchange on all times scales (with the constraint that p_A $\gg$ p_B), named after Ishima and Torchia (1999). It is selected by setting the model to `IT99'. The equation is:

$$\simeq {\frac{{\Phi_{\textrm{ex}}\tau_{\textrm{ex}}}}{{1 + \omega_a^2\tau_{\textrm{ex}}^2}}}$$ R_ex (11.30)

$$\sqrt{{\omega_{\textrm{1eff}}^4 + p_{\textrm{A}}^2\Delta\omega ^4}}$$ ω_a² (11.31)

R_2eff = R₂⁰ + R_ex. (11.32)

The effective rotating frame field for a CPMG-type experiment is given by

$$\sqrt{{3}}$$ (11.33)

and hence

ω_1eff⁴ = 2304ν_CPMG⁴. (11.34)

The reference for this equation is:

• Ishima and Torchia (1999)

More information about the IT99 model is available from:

• the relax wiki at http://wiki.nmr-relax.com/IT99,
• the API documentation at http://www.nmr-relax.com/api/3.2/lib.dispersion.it99-module.html,
• the relaxation dispersion page of the relax website at http://www.nmr-relax.com/analyses/relaxation_dispersion.html#IT99.