Role of the Renner-Teller effect after core hole excitation in the dissociation dynamics of carbon dioxide dication

Abstract

The fragmentation of the doubly-charged carbon dioxide molecule is studied after photoexcitation to the C 1s12πu and O 1s12πu states using a multicoincidence ion-imaging technique. The bent component of the Renner-Teller split states populated in the 1s→ π* resonant excitation at both the carbon and oxygen 1s ionization edges opens pathways to potential surfaces in highly bent geometries in the dication. Evidence for a complete deformation of the molecule is found in the coincident detection of C+ and \documentclass[12pt]{minimal}\begin{document}${\rm O}_2^+$\end{document}O2+ ions. The distinct alignment of this fragmentation channel indicates rapid deformation and subsequent fragmentation. Investigation of the complete atomization dynamics in the dication leading to asymmetric charge separation shows that the primary dissociation mechanisms, sequential, concerted, and asynchronous concerted, are correlated to specific fragment kinetic energies. The study shows that the bond angle in fragmentation can extend below 20°.

Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects

“…This is an additional confirmation that at the lower ion energies the molecular oxygen ion is formed in single ionization with low kinetic energy release, but in double ionization at higher energy. The fact that it is there formed with C + partner ions is not in doubt, as it was observed by Laksman et al 13 who investigated the dynamics in detail, and it is also confirmed here. But if the explanation given above for the formation of high kinetic energy O 2 + is correct, then C + (with O 2 ) ought to be formed by the same mechanism of electron recapture by O 2 + rather than by C + .…”

“…We focus first on the question posed by Laksman et al 13 whose ion-ion coincidence experiment is sensitive only to double (and higher order) ionization processes: is O 2 + produced from one or both of single or double ionization? As a first approach to this question we examine mass spectra coincident with different electrons.…”

“…This is also consistent with the localization of the π * orbital on the O atom. Both Laksman et al 13 and Öhrwall et al 7 also observed that O 2 + is produced less abundantly at the O1s-π * resonance than at the C1s-π * resonance. This might again be due either to a difference in the energy deposition function or to different behavior of specific states populated in the respective decays.…”

“…This reaction is not observed after ionization of CO 2 by other pathways; for comparison formation of S 2 + occurs in valence ionization of CS 2 , 26,27 but SO + is not detected from OCS valence ionization. 28 Laksman et al 13 also show by ion-ion correlation that at least some of the O 2 + arises from double ionization, as it is detected in coincidence with C + ions. They suggest that this may be its only formation pathway.…”

“…For highly excited or highly charged ions, although the total internal energy and the density of electronic states can be very much higher, some state-and site-specific behavior may still be expected. In a recent paper Laksman et al 13 show that ionization of CO 2 by initial excitation of a 1s electron from either the C or the O atom to a π * orbital, thus creating a highly excited state, results in formation of O 2 + ions, presumably by strong bending of the molecule. This reaction is not observed after ionization of CO 2 by other pathways; for comparison formation of S 2 + occurs in valence ionization of CS 2 , 26,27 but SO + is not detected from OCS valence ionization.…”