K-shell photoionization of CO and N<sub>2</sub>: is there a link between the photoelectron angular distribution and the molecular decay dynamics?

Weber, Thorsten; Jagutzki, O.; Hattass, M.; Staudte, A.; Nauert, A.; Schmidt, L. Ph. H.; Prior, M. H.; Landers, A. L.; Bräuning‐Demian, A.; Bräuning, H.; Cocke, C. L.; Osipov, T.; Ali, I; Muiño, R. Dı́ez; Rolles, Daniel; Abajo, F. Javier García de; Fadley, C. S.; Hove, M. A. Van; Cassimi, A.; Schmidt‐Böcking, H.; Dørner, R.

doi:10.1088/0953-4075/34/18/305

Cited by 116 publications

(78 citation statements)

References 34 publications

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“…1a. For this high KER the axial recoil approximation is known to be valid [18]. The transition to the 1 Π, 3 Π and 1 ∆ in region I shows an emission mainly perpendicular to the molecular axis, as one expects for a Π wave.…”

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confidence: 74%

“…2) which then couples to the first 3 Σ − curve leading to the ionic ground states. This corresponds to a dominant peak at 10 eV in the KER spectrum [17,18]. Similarly the structure around 251-255 eV Auger energy corresponds to a decay to the first [16] allow an assignment of the dominant channels in this region.…”

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confidence: 80%

“…We argue that this is a consequence of the failure of the axial recoil approximation. In a previous study of the photoelectron angular distribution coincident with a KER of 10 eV [18], we have shown that the CO 2+ for these decay channels lives long enough to rotate at least partially before fragmenting. In fact, the potential well in the second 1 Σ + supports at least two vibrational states which can be seen in a high resolution KER spectrum [17,18].…”

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confidence: 81%

“…(a) corresponds to the CO angular distribution, not shown here because of limited space, is also completely polarization independent. Since also here the CO + ion is known to rotate before decay [18] the angular distribution is almost without structure. This distribution is in agreement with the corresponding data in [1].…”

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confidence: 99%

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Auger Electron Emission from Fixed-in-Space CO

et al. 2003

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We have measured the angular distribution of Carbon K-Auger electrons from fixed in space, core-ionized, CO molecules in coincidence with the kinetic energy release of the C + and O + fragments . We find a very narrow ejection of Auger electrons in the direction of the oxygen and an oscillatory diffraction pattern. Even for similar electron energies, the angular distribution strongly depends on the symmetry of the final state. Our results do not support an earlier study (Guillemin et al [1]) which claimed observation of a breakdown of the two-step model of Auger and photoelectron emission.The study of Auger decay from molecules still pursues many open questions. One of the challenges results from the number and complexity of the final states. The many very broad overlapping structures in the Auger energy distribution often do not allow for a clear assignment of the decay channel [2]. A second challenge results from the interaction of the Auger electron with the molecular potential. Similar to photoelectrons [3,4] the Auger electron will be multiply scattered in the molecule hence modifying Auger rates and angular distributions. A third challenge was posed recently by the claim [1] that even off-resonance the creation of a core hole by photo-ionization and its subsequent Auger decay cannot be treated as two independent steps (two-step model), as has been commonly assumed [3,5].In the present letter we address these three challenges by reporting an experiment on the Auger decay of carbon K-shell ionized CO + . We have measured the Auger electron energy and angle in coincidence with the energy and angle of both fragment ions of the CO 2+ . Such complete monitoring of the process results in a qualitatively new level of insight into the molecular Auger decay. First the high resolution in electron energy and kinetic energy release (KER) allows determination of the final electronic states of the C + and O + fragments which in turn helps to identify the molecular decay channel. Second and more importantly, the measurement of the direction of fragmentation often, a posteriori, determines the molecular axis at the instant of Auger emission. We therefore obtain Auger electron angular distributions in * Electronic address: doerner@hsb.uni-frankfurt.de the molecular frame. These have, as we show below, a very rich structure. It has been emphasized from the theory side that the angular distributions from fixed in space molecules are a key to deeper understanding of the molecular Auger process [3,7,8]. Zähringer et al. have shown that the Auger electron angular distribution can be understood as resulting from two processes acting together. The symmetry of the molecular states involved and their nonspherical electron density lead to a coarse structure. On top of this a diffraction pattern from the interaction of the Auger electron wave with the molecular potential has been seen in the calculations. None of these effects have been observed experimentally until now [1,9].The experiment was performed at Bl 4.0 [10] of the Advanc...

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Auger Electron Emission from Fixed-in-Space CO

et al. 2003

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“…In the case of core or inner-shell photoionization followed by a single Auger decay, two valence electrons are lost in the final state and this condition, called ''axial recoil'' for diatomics, may or may not be satisfied [11]. However, because simultaneous double Auger decay is a strongly populated decay channel in methane, a substantial fraction of photoionization events produce a CH þþþ 4 trication from which three bonding electrons are…”

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Imaging Polyatomic Molecules in Three Dimensions Using Molecular Frame Photoelectron Angular Distributions

et al. 2012

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We demonstrate a method for determining the full three-dimensional molecular-frame photoelectron angular distribution in polyatomic molecules using methane as a prototype. Simultaneous double Auger decay and subsequent dissociation allow measurement of the initial momentum vectors of the ionic fragments and the photoelectron in coincidence, allowing full orientation by observing a three-ion decay pathway, (H þ , H þ , CH þ 2 ). We find the striking result that at low photoelectron energies the molecule is effectively imaged by the focusing of photoelectrons along bond directions. DOI: 10.1103/PhysRevLett.108.233002 PACS numbers: 33.80.Eh, 33.60.+q Imaging molecular structure is a critical challenge in chemical physics recently highlighted by the emergence of techniques that, similar to ultrafast electron diffraction [1] or x-ray diffraction [2], have the potential to be taken to the time domain and thereby ultimately be used to make ''movies'' of chemical reactions on their natural time scale. Of particular interest is the development of such techniques that can be applied to the dynamics of isolated molecules. Here, the full three-dimensional orientation of a polyatomic molecule is measured simultaneously with the three components of the momentum of a photoelectron ejected from it with no underlying assumptions of symmetry or geometry. We present three-dimensional images of a polyatomic molecule measured with this technique, demonstrating an effect predicted [3] for polyatomic molecules with a heavy central atom bonded to hydrogens, namely that low-energy photoelectrons can directly image the molecular potential and bond structure.When a photoelectron is launched by photoabsorption of an inner shell, the outgoing photoelectron wave is then scattered by the aggregate potential of the molecule. The final angular distribution in the body-fixed frame of the molecule is an exquisitely sensitive probe of molecular structure and initial electronic state, which has been recently argued and demonstrated [4,5]. However, observing molecular-frame photoelectron angular distributions (MFPADs) at high resolution requires accurate orientation of the molecule in the gas phase. Three-dimensional laser alignment [6,7] can accomplish such orientation prior to photoionization but is limited to molecules with an asymmetric polarizability. In the case of simple diatomic molecules, orientation can also be accomplished by detecting the photoelectron in coincidence with positively charged fragments that emerge following prompt Auger decay and dissociation [8]. Progress has also been made toward threedimensional MFPAD measurement using coincidence detection and velocity map imaging [9]. Here we present photoelectron imaging of methane molecules, where both the photoelectron momentum and corresponding body frame of the polyatomic molecule are fully determined in all three dimensions.For many molecules, including CH 4 , core ionization opens a strong simultaneous double Auger decay channel that produces a trication that then can disso...

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Molecular Inner‐Shell Spectroscopy. ARPIS Technique and its Applications

Shigemasa

Kosugi

2011

Advances in Chemical Physics

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K-shell photoionization of CO and N₂: is there a link between the photoelectron angular distribution and the molecular decay dynamics?

Cited by 116 publications

References 34 publications

Auger Electron Emission from Fixed-in-Space CO

Auger Electron Emission from Fixed-in-Space CO

Imaging Polyatomic Molecules in Three Dimensions Using Molecular Frame Photoelectron Angular Distributions

Molecular Inner‐Shell Spectroscopy. ARPIS Technique and its Applications

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K-shell photoionization of CO and N2: is there a link between the photoelectron angular distribution and the molecular decay dynamics?

Cited by 116 publications

References 34 publications

Auger Electron Emission from Fixed-in-Space CO

Auger Electron Emission from Fixed-in-Space CO

Imaging Polyatomic Molecules in Three Dimensions Using Molecular Frame Photoelectron Angular Distributions

Molecular Inner‐Shell Spectroscopy. ARPIS Technique and its Applications

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Product

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K-shell photoionization of CO and N₂: is there a link between the photoelectron angular distribution and the molecular decay dynamics?