What happens if the s—p separation is small

Since the MO approach is a theoretical model, what experimental evidence is there for this tr-Tr crossover The actual electronic configurations of molecules are nearly always determined spectroscopically, particularly by 

Chapter 1 Homonudear diatomic molecules molecular orbital (MO) theory 35 

Worked example 1.8 Molecular orbital theory properties of diatomics 

The bond dissociation enthalpies for the nitrogen-nitrogen bond in N2 and [N2] are 945 and 765kJmol respectively. Acconnt for this difference in terms of MO theory, and 

The lower bond order of [N2] compared with N2 is consistent with a lower bond dissociation enthalpy. 

Diatomic Bond distance / pm Bond dissociation enthalpy / kJ mop Bond order Magnetic properties 

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