More on Asymptotic behaviors of 9j Coefficients
  Previouslywe noted in numerical calculations that a certain unitary ninej coefficient U9j =((jj)^{2j} (jj)^{2j} | (jj)^{2j} (jj) ^{(2j-2)})^{I} decreases with increasing j and for small I the decrease is of the form C j^{m} e^{-\alpha j} . The exponential decay dominates. It is here shown that \alpha = 4 ln(2) and m=3/2. 
Brian Kleszyk and Larry Zamick
nucl-th physics.atm-clus physics.atom-ph quant-ph