Water molecule photoelectron spectrum

Appelman has reviewed the case history of HOF, the recently isolated non-existent molecule, which may well be the reactive species formed when F2 reacts with water. The photoelectron spectrum of this unstable compound has been obtained by Berkowitz et al using He I resonance radiation. Three bands were observed which could be interpreted by analogy with the diatomic halogens and with the recently reported CIF. The first (adiabatic) ionization potential was found to be 12.69 0.03 eV, in close agreement with the photoionization value of 12.7 0.01 eV. 

Experimental confirmation of the order of MO energies for the water molecule is given by its photoelectron spectrum. Figure 5.13 shows the helium-line photoelectron spectrum of the water molecule. There are three ionizations at 1216, 1322 and 1660 kJ mol1. A fourth ionization at 3107 kJ mol-1 has been measured by using suitable X-ray photons instead of the helium emission. That there are the four ionization energies is consistent with expectations from the MO levels for a bent C molecule (see Figure 5.12). 

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