THEORY OF PULSES IN NUCLEAR-QUADRUPOLE RESONANCE SPECTROSCOPY .1. PHYSICAL PICTURE

The effect of radiofrequency pulses in nuclear quadrupole resonance (NQR) spectroscopy is examined. The description is different from that needed in nuclear magnetic resonance (NMR) spectroscopy. In particular, both rotating and counter-rotating radiofrequency field components are retained. Pulses in NQR spectroscopy are selective and cause transitions between two pairs of levels (+/-M) --> +/-(M + 1), other transitions are not normally excited. The formulation of pulses is then described for any spin I by two 2 x 2 rotation matrices, one causing an M --> M + 1 transition and the other causing a -(M + 1) --> -M transition. Calculations on resonance for spins with an axially symmetric nuclear quadrupole for up to three pulses are presented for spins I = 1 and I = 3/2. The results agree with the work of Reddy, R. and Narasimhan, P. T., 1991, Molec. Phys., 72, 491, in the appropriate limits.