Ionization energies have been obtained for all the valence orbitals of some simple hydrocarbons and also some of their isoelectronic analogues in which a nitrogen or an oxygen atom replaces CH or CH₂ respectively. This required the use of a helium discharge run under conditions such that a high proportion of 30.4 nm radiation was emitted. In order to utilize the full range of the 41 eV photon it was further necessary to use filters, usually polystyrene films about 100 nm thick, selectively to absorb 58.4 nm radiation.

Analysis of the results show that in many molecules the summed binding energies of the molecular orbitals built from 2s atomic orbitals may be divided up into atomic contributions which agree in magnitude with those obtained for the same atoms in other molecules, i.e., the atomic contributions are additive as is expected from the application of simple theory. A similar additive behaviour was also found for the orbitals built from 2p and 1s(H) atomic orbitals though theory does not directly indicate this for incompletely filled orbital systems of this type.

Certain weak photoelectron bands have been found at high energies which arise from transitions to configurationally mixed ionized states. The experimental results are compared with theoretical predictions.