The nuclear scattering at energies well above the Coulomb barrier allows for a fairly sensitive examination of the parameters of the optical potential when the relevant couplings are included into the calculations. In this work we present experimental angular distribution data for the elastic and inelastic scatterings of ^16O impinging on ^27Al and ^28Si target nuclei at E_lab=240 MeV. The experimental data were measured at 7 < θ_c.m. < 16 with good angular resolution. Experimental data are

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... ared with coupled channel calculations with the inclusion of couplings to excited states in the target and projectile. We show that the shape of angular distributions are sensitive to the mass diffuseness parameter and the best agreement is achieved for a = 0.62 fm.