Conclusions

In this work, we have substantially advanced the experimental and theoretical understanding of ozone in the regime of valence double photoionization. By combining He II-α, He II-β, and higher-energy vacuum ultraviolet radiation with a versatile multiple charged-particle correlation detection technique, we recorded the first single-photon valence double-ionization electron spectrum of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm {O_3}$$\end{document} and obtained detailed insight into the fragmentation dynamics of the resulting dicationic states. The measured double-ionization energies provide valuable experimental benchmarks for future theoretical descriptions of multiply ionized ozone.

To interpret the experimental observations, we mapped the lowest potential energy surfaces of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm {O_3^{2+}}$$\end{document}using state-of-the-art post-Hartree–Fock multiconfigurational methods and determined with high accuracy the energetics of the relevant dissociation channels. The combined experimental and theoretical results reveal that dissociative double ionization of ozone proceeds not only through the formation of ground-state O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}_2^+$$\end{document} + O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^+$$\end{document} fragments, but also through pathways involving electronically excited O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^+$$\end{document} ions or O atoms. The energetics of the first part of the double ionization spectrum of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm {O_3\rightarrow O_2^++O^+}$$\end{document} combined with the found KER reveals that both O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}_2^+$$\end{document} and O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^+$$\end{document} fragments dissociate in the ground electronic state. The energetics of the 38 eV band of the same process suggests that the outgoing O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^+$$\end{document} is electronically excited to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^2$$\end{document}D and that the O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}_2^+$$\end{document} fragment has substantial vibrational energy of about 1 eV. The potential energy surfaces presented also show that some dissociations above 37 eV double ionization energy result in an electronically excited O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}_2^+$$\end{document} (a\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^4\Pi _u$$\end{document}) and the ground state O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^+$$\end{document} (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^4$$\end{document}S). These findings uncover a level of complexity in the fragmentation dynamics of doubly ionized ozone that has not previously been recognized.

Beyond providing a detailed picture of ozone dication decay, the present results offer new insight into the redistribution of energy following molecular double ionization, a process of fundamental importance in radiation-driven environments. The observation of electronically excited oxygen fragments is particularly significant, as such species can initiate highly reactive chemical pathways in planetary atmospheres. In this respect, the processes identified here may represent an ionization-driven analogue to the well-known production of O(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\vphantom{0}^1$$\end{document}D) atoms in ozone photodissociation, highlighting a potentially overlooked source of chemical activation under intense ionizing radiation.

Overall, this study establishes the first comprehensive framework for understanding valence double ionization and subsequent fragmentation in ozone. By combining high-resolution experiment and advanced electronic-structure theory, it not only provides definitive benchmarks for future investigations of ozone dications, but also opens new avenues for exploring the role of multiply ionized molecules in atmospheric, planetary, and astrochemical environments.