Adiabatic fast passage (AFP) pulses 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.

Thus, broadband adiabatic decoupling is more efficient than conventional composite-pulse decoupling, in terms of average power deposition for large bandwiths. Some advantages are:

More iInsensitive 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

    Several adiabatic decoupling schemes have been proposed:

STUD schemes that use sech/tanh adiabatic 180 inversion pulses ( 96JMRA77-120 , 97JMR474-124 , 98JMR315-134 , 98JMR331-134 , 94JMRA24-107 , 95JMRA126-112 , 95JMRA46-116 , and 96JMRA111-123 ).

CHIRP schemes ( 95CPL415 , 95JMRA46-116 , 95JMRA324-117 , and 96JMRA129-119 ) where inversion is achieved adiabatically by a Chirp pulse with linear frequency modulation.

WURST schemes ( 95JMRA273-115 , 95JMRA246-117 , 96CPL523 , and 96JMRA299-118 ).

Frequency-switched MPFn ( 88JMR53-77 and 93JMRA103-104 ) and frequency-phase-modulated pulses ( 90JMR584-86 ).

Other approaches: 97JMR250-124 , 96JMRA133-120 , and 94JMRA241-106 .

A serious drawback can be the generation of strong cyclic sidebands that reduce the sensitivity of the method . Several approaches have been proposed to reduce such inconvenients:

• Bilevel decoupling ( 96JMRA81-122 )
• By varying decoupling periods ( 96JMRA221-121 )
• Adiabatic defocusing ( 97JMR219-129 )
• Gradient dephasing applied just before acquisition ( 97JMR30-129 )
• Use of ECHO-WURST ( 97JMR36-127 )
• A 2D approach to separate decoupling sidebands from the main pekas (01JMR142-151).
• Phase cycling algorithms (97JMR474-124 and 00JMR316-144.

Especially useful are AFP pulses when used for selective rofocusing or in NMR experiments involving manipulations of 13C spins with their broad chemical shift range. Application on 2D HSQC, 3D HCCH-TOCSY and 3D CBCA(CO)NH experiments have been reported ( 99JB331 ).