The 3d bound orbital and two examples of ef continuum wavefunctions

For molecules, the problem is more complex than for atoms because the continuum must usually be expressed as a sum of many partial waves. It is highly unlikely that the Cooper minima for all of the important /-partial wave components will occur near the same value of e. An example of a Cooper minimum in a molecular photoionization cross section is observed for HI, corresponding to ionization from the 5p7t orbital (Carlson et al., 1984). Other examples of Cooper 

In Section 8.11, the influences of shape resonances and Cooper minima on photoelectron angular distributions will be discussed. 

Above ionization limits, lines in the absorption spectrum are often broad or diffuse. This diffuse character results from an interaction of a very highly excited neutral molecule state, AB, with the continuum of an ionized molecule, AB+, plus an electron. This continuum reflects the fact that the electron can be ejected from the molecule over a continuous range of kinetic energy  

The state AB, often called the superexcited state, is an autoionized or resonance state. Autoionization is called preionization by Herzberg (1950). This can be justified by the analogy between preionization and predissociation. In predissociation, the interaction of a discrete state with the vibrational continuum of the nuclei allows this discrete state a finite probability of dissociation. In preionization, it is the mixing of a discrete state with the electronic continuum that provides a finite ionization probability. 

We consider in the following the case of a single isolated resonance, far removed from other resonances. If an absorption line has a Lorentzian profile, the linewidth/ T, is related to the total lifetime, r, of the state by the usual relation P oc r 1 [cf. Eq. (7.4.11)]. This width includes contributions from each of these three different types of decay. If interactions between continua of the electron, nuclei, and radiation field are neglected, one can write 

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Figure 8.7 The 3d bound orbital and two examples of ef continuum wavefunctions (at e as 0 a.u. and e as 3 a.u. (from Manson and Cooper, 1968).

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