Size effects in multiple quantum NMR of finite spin chains

Exact calculations of multiple quantum NMR spectral intensities in finite one-dimensional quantum spin chains with nearest-neighbor couplings and evolving under a two-quantum/two-spin propagator reveal a transition between regular and erratic behavior in the spin dynamics. The onset for this transition, which depends on the number of spins in the chain, arises from spin wave packet propagation and reflection which produce interference effects in finite chains. Implications for excitation of high-order coherences in solids are discussed. The perturbations of one and two spins on the multiple quantum NMR response of an N-spin chain are also examined.