Exact results on spin dynamics and multiple quantum dynamics in alternating spin - 1 2 chains with XY - Hamiltonian at high temperatures

We extend the picture of a transfer of nuclear spin2 polarization along a homogeneous one-dimensional chain with the XY -Hamiltonian to the inhomogeneous chain with alternating nearest neighbour couplings and alternating Larmor frequencies. To this end, we calculate exactly the spectrum of the spin2 XY -Hamiltonian of the alternating chain with an odd number of sites. The exact spectrum of the XY -Hamiltonian is also applied to study the multiple quantum (MQ) NMR dynamics of the alternating spin2 chain. MQ NMR spectra are shown to have the MQ coherences of zero and ± second orders just as in the case of a homogeneous chain. The intensities of the MQ coherences are calculated.