Using quaternions to design composite pulses for spin-1 NQR

The fictitious spin-1/2 operators are well known to describe the evolution of a pure nuclear quadrupole resonance (NQR) system; particularly, the application of a radio-frequency pulse at one of the NQR transition frequencies is equivalent to a three-dimensional rotation in a space defined by the corresponding fictitious spin-1/2 operators. We demonstrate, theoretically and experimentally, that consecutive noncommuting rotations applied at the same transition frequency are well described by a single rotation given by quaternion parameterization of the rotations in ficitious spin-1/2 operator space. This new route could greatly save computing time and efforts. We extend this approach to design composite pulses that compensate for the effects of the radio-frequency field inhomogeneity for a powder sample of spin-1 nuclei.