Three-body fragmentation of $\mathrm{C}\mathrm{O}_2{}^{2+}$ upon $K$-shell photoionization

The fragmentation dynamics of $\mathrm{C}{\mathrm{O}}_2$ molecules subsequent to $K$-shell photoexcitation and ionization was studied using a multicoincidence ion momentum imaging technique. The detailed analysis via fragment momentum correlation plots (Newton diagrams) clearly reveals concurrent fragmentation mechanisms for the three-body dissociation of $\mathrm{C}\mathrm{O}_2{}^{2+}$ into ${\mathrm{C}}^{+}+{\mathrm{O}}^{+}+\mathrm{O}$, for both linear and bent geometry states of $\mathrm{C}\mathrm{O}_2{}^{2+}$. The experimental results are supported by a classical trajectory simulation based on a Coulomb explosion model, which elucidates energy and angular correlations between fragments for different fragmentation processes.

Figure 1

(Color online) KER for different fragmentation channels of $\mathrm{C}\mathrm{O}_2{}^{2+}$: (a) $\mathrm{C}{\mathrm{O}}^{+}+{\mathrm{O}}^{+}$ (left), (b) $\mathrm{C}+{\mathrm{O}}^{+}+{\mathrm{O}}^{+}$ (middle), and (c) ${\mathrm{C}}^{+}+{\mathrm{O}}^{+}+\mathrm{O}$ (right). The energy of the neutral fragments is deduced from the experimental data by applying momentum conservation. The photon energy was set to the O $1s^{-1}2{\pi }_u$ resonance at 535.4 (lower row) and $7.6\mathrm{eV}$ (upper row) below the resonance.

Figure 2

(Color online) (a) Newton diagrams for $\mathrm{C}\mathrm{O}_2{}^{2+}$ fragmenting into $\underset{̱}{{\mathrm{O}}^{+}}+\mathrm{C}{\mathrm{O}}^{+}$ (left), $\mathrm{C}+\underset{̱}{{\mathrm{O}}^{+}}+{\mathrm{O}}^{+}$ (middle), and $\underset{̱}{{\mathrm{C}}^{+}}+{\mathrm{O}}^{+}+\mathrm{O}$ (right) fragmentation channels. The reference ion (represented by the arrow in the middle diagram) is underlined. (b) Angle between coincident fragments detected for the above fragmentation channels. (c),(d) Newton diagrams plotted for different energy intervals (labeled above diagram) of ${\mathrm{C}}^{+}$ (c) and ${\mathrm{O}}^{+}$ (d) reference ions on the O $1s^{-1}{\pi }^{*}$ resonance and $7.6\mathrm{eV}$ below it.

Figure 3

(Color online) Results of the CE model for the ${\mathrm{C}}^{+}+{\mathrm{O}}^{+}+\mathrm{O}$ fragmentation channel for concerted, sequential, and deferred fragmentation and different lifetimes of the intermediates. The angle between ${\mathrm{C}}^{+}$ and ${\mathrm{O}}^{+}$ ions and the kinetic energy of ${\mathrm{C}}^{+}$, ${\mathrm{O}}^{+}$ and O fragments is calculated as a function of the bond angle. The scatter of the calculated points is caused by the rotational and vibrational motion.