A mixed supersymmetric-algebraic approach is employed to derive an improved Kratzer-Fues energy formula, which describes the highly excited states of vibrating diatomic systems. The approach proposed has been used to reproduce the coherent anti-Stokes Raman spectra generated by the vibrational transitions (ν < 6) of the nitrogen molecule 14N2 in the ground electronic state X1Σ+g and the energy levels (v < 42) of dioxygen 16O2 in the ground electronic state X3Σ− g . The model includes v-dependence of the potential depth D0 → Dv and interatomic equilibrium separation r0 → rv and can be used to describe vibrations of diatomic molecules in which nonadiabatic vibrational effects play a significant role.