COMPLETE SPIN DYNAMICS OF THE AX, AX(2) AND AX(3) SPIN SYSTEMS - APPLICATION TO BIRD PULSES

The BIRD pulse sequence is widely used to distinguish between protons that are directly bonded to a C-13 nucleus and those that are not. It consists of a proton 90 degrees pulse, a delay of 1/(2(1)J(CH)), simul taneous carbon and proton 180 degrees pulses, a further delay of 1/2J and a final proton 90 degrees pulse. For two spins at equilibrium, the effect of this sequence can be easily understood, but for complex sys tems the behaviour can be counter-intuitive. This paper explains the g eneral behaviour of the BIRD sequence using theoretical equations and numerical simulations, and discusses some practical applications of th e BIRD pulse train. The theoretical equations are derived using tables of general behaviour for the spin systems AX, AX(2) and AX(3). The ta bles allow the exact calculation of the effect of any pulse sequence o n these spin systems, including an multiple quantum effects. The simul ations show that the sequence is usually robust with respect to pulse imperfections and non-ideal spin systems. In other cases, particularly when signals should be suppressed, small errors can have dramatic con sequences. The results derived here are for a BIRD sequence inserted i nto an INEPT experiment, but many of the conclusions can be applied to all of the more standard applications of the BIRD.