A comparative study of the influence of the chemical bond on the photo-ionization cross section at a distance from the threshold

1979 ◽  
Vol 20 (3) ◽  
pp. 355-360
Author(s):  
I. G. Kaplan ◽  
V. N. Smutnyi

The absorption of radiation of wave-length between 230 and 800 Å in neon was measured photometrically in a grazing incidence vacuum spectrograph. For wave-lengths longer than that corresponding to the first ionization limit the absorption coefficients were found to be zero except for photo-excitation of resonance transitions. Two sharp absorption edges were observed at 575 and 256 Å corresponding to the L 3 - and L 1 -edges respectively with a flat maximum between them. The photo-ionization cross-section at the first ionization limit was found to be 5⋅4 x 10 -18 cm 2 independent of the pressure between 50 and 500 μ ; this should be compared with the theoretical value of 5⋅8 x 10 -18 cm 2 obtained by Seaton using a dipole-length approximation. Between 575 and 400 Å the calculated and experimental curves agreed closely within the limits of measurement.


The photo-ionization of atomic potassium is investigated using quantal methods. Emphasis is laid on the great sensitivity of the cross-section to the wave functions employed. The general features of the cross-section as revealed by the laboratory measurement can be understood. To explain the finite minimum observed in the cross-section-frequency curve it is necessary to take into account non-separability effects.


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