Hyperspherical asymptotics of a system of four charged particles
  We present a detailed analysis of the charged four-body system in hyperspherical coordinates in the large hyperradial limit. In powers of $R^{-1}$ for any masses and charges, the adiabatic Hamiltonian is expanded to third order in the dimer-dimer limit and to first order in the particle-trimer limit. 
K. M. Daily
physics.atom-ph