Interpretation of Photoionization Threshold Behavior

Abstract
Analytical expressions are derived for treating the threshold regions of photoionization efficiency curves. The effects of slitwidth, the initial thermal energy of the molecular system, and Franck–Condon factors are considered. In the dissociative ionization of small molecules such as F2 and HCN, discrepancies can arise from failure to take these factors into account. It is also shown that for large polyatomic molecules, the use of a Watanabe-type plot to determine the adiabatic ionization potential can lead to large errors. The paper concludes with detailed applications to HF, O2, S2, Se2, Te2, S6, and S8, and some general observations applicable to the diatomic halogens, hydrogen halides, and alkali halides.

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