Two-magnon states in Cu(NO3)2*2.5D2O using inelastic neutron scattering
  We report measurements of the two-magnon states in a dimerized antiferromagnetic chain material, copper nitrate (\QTR{group}{Cu(NO$_{3}$)$_{2}\cdot 2.5$D$_{2}$O}). Using inelastic neutron scattering, we have studied the one- and two-magnon excitation spectra in a large single crystal of this material. We compare this new data with perturbative expansions of the alternating Heisenberg chain and find good agreement with these calculations. The data may also show evidence for the recently proposed S=1 two-magnon bound state (Phys. Rev. B54, R9624 (1996)). 
D.A. Tennant, C. Broholm, Daniel H. Reich, S.E. Nagler, G.E.Granroth,   T. Barnes, G. Xu, B.C. Sales and Y. Chen