Ultraviolet photoelectron spectra of molecules

From the separations of the progression members the vibrational constants cOg, copcg, cOgyg. (Equation 6.16) for FiJ can be obtained. Comparison of cOg = 2322 cm for the state of FiJ with cOg = 3115 cm for the state of FI2 shows that the 

From the separations of the progression members the vibrational constants coe, cOgXe, (oeye. (Equation 6.16) for II) can be obtained. Comparison of coe = 2322 cm-1 for the X2Zg state of II) with coe = 3115 cm 1 for the XlZg state of H2 shows that the vibrational force constant (see Equation 6.2) is much smaller in the ground state of H) than in H2. This, in turn, implies a weaker bond in H) consistent with the removal of a bonding electron. 

It is the vertical ionization energy to which Koopmans theorem refers (Equation 8.5). 

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