Photoionization open shell atom

The problem of photoionization of open-shell atoms is rather difficult, and, as a result, the number of calculations and particularly of experiments is limited. The R-matrix method has been used to calculate detailed cross sections of open-shell atoms such as Al O, N, and 0. In the R-matrix method,... 

Closed-shell atoms are considered here, because in open-shell systems the photoionization process is generally determined by more than three matrix elements (five parameters). 

The majority of recent PES studies of the halomethanes has concerned photoionization dynamics, and has employed synchrotron radiation sources. Halomethanes are aptly suited for such studies because they exhibit a relatively small number of well-resolved PES bands and contain atoms of very different atomic number, Z. This variation of Z permits fine tuning of the molecular ion potential and opens a window for the study of photoelectron-ion interactions. In addition, the Br3d and I4d shells have large photoionization cross-sections in the SXR region, thus extending the scope of PES studies from the valence to the outer-core electrons. 

For larger clusters much spectroscopic detail is lost, but measurements of the photoionization thresholds provide information concerning cluster ionization potentials. Sodium clusters show a relatively smooth decrease in ionization potential from 5.1 eV for the atom to 3.5 eV for the 14-atom cluster. This is still significantly above the 1.6-eV work function of bulk sodium. For the smaller clusters the odd sizes have a lower ionization potential than the neighboring even-sized clusters because of effects due to open versus closed shell configurations. Recently measurements have been made of the ionization potential of iron clusters up to 25 atoms. In this experiment the ionization potentials were bracketed by the use of various ionizing lasers. There is a decrease in the ionization potential from 7.870 eV for an iron atom to the 4.4-eV work function of the bulk metal, but the trend is by no means linear. Thus, the ionization potential of Fea is about 5.9 eV, while those of Fes and Fe4 are above 6.42 eV. Clusters in the range of 9-12 atoms have ionization potentials below... 

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