Adiabatic fast passage (AFP) pulses (97NMRB423, 97JMR36-127, 98JMR169-130, 99JMR173-138, 01JMR155-153 and 02JMR26-156) are specially suited for 180 rotations because they provide basically unlimited bandwidth and accurate flip angles with high tolerance to spatial variations in RF field intensity. Adiabatic pulses invert spins by a slow passage of a chirped pulse through resonance. So spins having a different resonance frequency will be inverted at different times. This differs from th ebhavior during a square pulse, where all spins are inverted simultaneously.

Some advantages are:

More insensitive to RF miscalibration and, therefore, high tolerance of spatial inhomogeneity

Accurate spin inversion over a large range of RF power levels

Minimization of decoupling power and sample heating

Type of adiabatic pulses:

sech/tanh (or hyperbolic secant)

tanh/tan

Applications:

Spin inversion.

Refocusing in 1H-13C HSQC, 3D HCCH-TOCSY and 3D CBCA(CO)NH experiments using hyperbolic-secant (HS) pulses (95JB59 , 99JB331 )

Application to broadband TOCSY sequences with C,C or H,H J-transfer (00JB199-18 , 98JMR361-135 , 01MRC231 , 01JMR115-148 ) (For instance, in HCCH-TOCSY experiment.

Inversion in X-filter for isotope editing ( 96JB492-8 , 97JACS6711 )

Effect of spin-spin coupling during adiabatic pulses ( 97JMR36-127 )

Broadband adiabatic decoupling

Broadband, selective excitation using frequency-modulated pulses ( 02JMR131-155 )

General reading on adiabatic pulses in:

Biomolecular NMR ( 01METH82

Biomedical NMR applications (02CONC89)