Reexamine Valence Correlation Scheme for Yrast 2^+ States When Valence Nucleons in the Same Shell

The variation of excitation energies E_2^+ of yrast 2^+ states and ratios R=E_4^+/E_2^+ with neutron number N , valence neutrons N_n / N_ν and valence protons N_p / N_π of nuclei having valence nucleons in the same shell is studied. It is noticed that the depression in E_2^+ and ascension in R appear in isobars that differ from the predictions of the N_pN_n scheme in which isotones are expected. The depression in E_2^+ and ascension in R can be correlated with the number of valence nucleons M_T , N_p=N_n and ( N_pN_n) _max depending on the isotope and mass region considered, where M_T is the half of the total number of valence nucleons that can be accommodated in the considered shell.