Masses of $nS$-wave Heavy Quarkonium Levels from QCD Sum Rules
  Using a specific scheme of the QCD sum rules, one derives an universal formula for the mass differences for the $nS$-levels of heavy qiarkonium. This relation does not depend on the flavours of the heavy quarks, composing the quarkonium, and it is in a good agreement with the experimental mass values for the $\psi$- and $\Upsilon$-families. 
V.V.Kiselev