We describe a method that allows the measurement of absolute photoionization cross sections with a simple experimental setup. In a barium oven designed as a thermionic diode, ions are produced by use of a two-step pulsed-laser excitation and ionization combined with optogalvanic detection. The variation of the photoionization cross section of the excited BaI 6s6p ¹^∘₁ state is measured versus wavelength. At threshold the cross section is (5±{}2)×{}10^-20 m². In the experiment strong evidence for the existence of Ba₂⁺ dimers was found.
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Kallenbach et al. (1988) studied this question.
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