The IT99 2-site CPMG model

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

Rex $\displaystyle \simeq$ $\displaystyle {\frac{{\Phi_{\textrm{ex}}\tau_{\textrm{ex}}}}{{1 + \omega_a^2\tau_{\textrm{ex}}^2}}}$, (11.30)
ωa2 = $\displaystyle \sqrt{{\omega_{\textrm{1eff}}^4 + p_{\textrm{A}}^2\Delta\omega ^4}}$, (11.31)
R2eff = R20 + Rex. (11.32)

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

ω1eff = 4$\displaystyle \sqrt{{3}}$νCPMG, (11.33)

and hence

ω1eff4 = 2304νCPMG4. (11.34)

The reference for this equation is:

More information about the IT99 model is available from:

The relax user manual (PDF), created 2024-06-08.