Eigenvalues occurring from approximations

Hie canonical MOs of a planar unsaturated organic molecule can be divided into molecular plane is +1 or -1, respectively (Section 15.10). The earliest semiempirical methods for planar conjugated organic compounds (Sections 16.2-16.4) treated the tt electrons separately from the cr electrons. Coulson stated that the justification for the ct-tt separability approximation lies in the different symmetry of the cr and tt orbitals and in the greater polarizability of the tt electrons, which makes them more susceptible to perturbations such as those occurring in chemical reactions. 

Extensive information on weakly bound, physisorbed atoms on solids is available from bound state resonance data obtained from beam scattering experiments. Strong changes in the scattering intensities are observed when selective adsorption in the physisorption well occurs (see, for instance, ref. [113]). The resonance positions yield the eigenvalues E of the potential V(z). These satiesfies to a good approximation the Bohr-Sommerfeld quantization condition... 

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