The BIRD (from Bilinear Rotational Decoupling) operator is a group of pulses that permit discrimination on the basis of the size of ¹H-¹³C coupling constants ( 82CPL504 ) . Differentiation is based on the fact that the direct ¹H-¹³C coupling constant (¹J_CH) is in the range from 125-220 Hz while long-range ¹H-¹³C coupling constants (¹J_CH)  are generally less than 15 Hz. There are basically two alternatives. In the first, all protons directly bonded are inverted while protons long-range coupled are unaffected. In the second, the protons long-range coupled are inverted and the direclty-bonded unaffected. The difference between this two versions of the BIRD cluster lies in the phase of the final 90º proton pulse.

Several BIRD applications hace been reported:

• Selective observation of ¹J_CH vs ⁿJ_CH coupling constants.
• Decoupling modulations due to ¹J_CH in long-range heteronuclear chemical shift correlations.
• Supression of unwanted ¹H-¹²C magnetization in inverse spectroscopy (see BIRD-recovery cluster).
• Decoupling of homonuclear scalar interactions in heteronuclear experiments.

Other related BIRD pulse trains have been reported for simultaneous and independent rotations with arbitrary flip angles and phases for I and IS spin systems: BIG-BIRD ( 97JMR202-125 ) and TIG-BIRD ( 98JMR44-135 ) elements

Easy implementation on AVANCE spectrometers.

 The interpulse delay d2 is set to 1/(2*J_CH)

The standard way to implement a BIRD cluster is:

... (p3 ph1):f2 d2 (p4 ph2):f2 (p2 ph3) d2 (p3 ph1):f2 ...

in which p3 and p4 are the 90 and 180 degree decoupler 1H pulses, p2 is the 180 degree transmitter 13C pulse, d2 is the delay optimized to 1/(2J(XH)) and the phases are ph1=1, ph2=0 and ph3=0.