The comparison of the ionization yield from the Jesse effect <tex-math>$\eta _{{\rm J}}$</tex-math> and the photoionization yield <tex-math>$\eta _{{\rm P}}$</tex-math>, as first made by Platzman, is updated, with a graphical comparison shown for the case of benzene. The majority of examples show <tex-math>$\eta _{{\rm J}}\approx \eta _{{\rm P}}$</tex-math> and most of the other <tex-math>$\eta _{{\rm J}}$</tex-math> values are about 10-20% lower than the <tex-math>$\eta _{{\rm P}}$</tex-math> values. Isotope effects are also compared and the <tex-math>$\eta _{{\rm J}}$</tex-math> data are used to estimate the fraction of ionization via direct ionization. The implications of these comparisons are discussed, particularly those concerning the nature of the Jesse precursors. In addition, the use of different ionization chamber geometries is suggested as a means of testing the importance of escape of vacuum ultraviolet radiation as a decay process for the Jesse precursors.

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