Abstract
The issue of the ratio R=Γ(ψ→γη’)/Γ(ψ→γη) and the η-η’ mixing angle θ is discussed in an approach on the basis of chiral and large-Nc arguments. Gluonic matrix elements αs〈0‖GG̃‖η(η’)〉 are estimated. θ≃-20° is found to be strongly favored over θ≃-10°, and is in agreement with the experimental value of R.