On the relations between two-photon and leptonic widths of low-lying   S-wave states of charmonium
  The relation between the ratio Gamma_{ee}(psi')/Gamma_{ee}(J/psi) and Gamma_{2gamma}(eta_{c}')/Gamma_{2gamma}(eta_{c}), expressed in terms of the configuration mixing amplitudes induced by the contact spin-spin interaction of quarks in the ground and radial excitation states, is shown to give, after the inclusion of the newly derived relativistic corrections, the radiative eta_{c}'- and \eta_c-width ratio in fair accord with recent experiments. The dynamical model is proposed to derive the ratio of relative probability of the ground (eta_{c}(2980))- and first radial excitation (eta_{c}'(3640))-state formation in gamma-gamma collisions followed by their decay into the pi\bar{K}K and p\bar{p} channels. 
S.B.Gerasimov and M.Majewski