Homogeneous FID signals in polypyrroles: T-1-estimate from a two-pulse sequence in homogeneous systems

Several experiments using pulse electron spin resonance (ESR) equipment rev eal that homogeneous free induction decay (FID) signals are given by electr on spins in polypyrrole (PPy). FID signals obtained from PPy are accurately fitted via single-exponential curves, thus indicating that PPy can be used as a standard sample for several experiments with pulse ESR. We particular ly pay attention to the nutation phenomena resulting from two-pulse irradia tion (theta-t-2 theta-t) in the homogeneous systems. The analysis by the ve ctor model suggests that the nutation curves are affected by spin-lattice r elaxation; Such a tendency is actually observed for two types of PPy used a s examples of T-1 > T-2 and T-1 approximate to T-2. Thus the fitting over t he nutation curve can be utilized for estimating T-1. We particularly point out that such a procedure can be advantageously performed for electron spi ns with a short spin-lattice relaxation time.