The response of a spin 7 2 in solids, subject to a first-order quadru-these echoes (''forbidden'' echoes) arise exclusively from polar interaction, to a spin lock pulse sequence is calculated. The the refocusing of MQ transitions. results are valid for any ratio of quadrupolar coupling, v Q , to In this paper we use the same pulse sequences employed the amplitude, v 1 , of the RF pulse. It is shown here that the for spins 3 2 and 5 2 in (15) to investigate MQ transitions for measurements of the central line intensity as a function of the spin 7 2 . These two-pulse sequences include various phase second pulse length can be used for the determination of quadrupocyclings as well as a combination of spin lock and spin lar parameters using various phase cycling techniques. It is proven echo pulse sequences. The first-order quadrupole is retained that the DQ coherences developed during the first pulse can be throughout and, in particular, in the calculations of pulses. selectively detected. แญง 1997 Academic Press
Thus our results are applicable to symmetrical (i.e., featureless) lineshapes. However, the measurement of the integrated areas of the central line as a function of the second