Selection Rules and Isotope Effects in the Full Fragmentation of the Hydrogen Molecule

Walter, Michael; Js, Briggs

doi:10.1103/physrevlett.85.1630

Cited by 24 publications

(33 citation statements)

References 8 publications

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“…For other geometries we find that the angular distributions are almost completely dominated by the interplay between the electron-electron repulsion and the angular momentum and parity selection rules [12,22]. 5 An atomic photo-ionization cross section can be described by a dipole distribution with its symmetry axis in the direction of the polarization of the incoming photon.…”

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confidence: 99%

Complete photo-fragmentation of the deuterium molecule

Weber

Czasch

Jagutzki

et al. 2004

Nature

154

132

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However, despite 80 years of theoretical attention, near exact calculations for such systems are only available for bound states. On the experimental side, the tests of these calculations are largely based upon level energies or single particle momentum 3 distributions. Very promising and challenging new classes of experiments are those which achieve a complete description of the outcome following the excitation of the ground state to an unbound continuum. The momenta, i.e. the set of vectors, of all the fragments of an atom or molecule break-up can be measured in coincidence with high precision using state-of-the-art imaging and timing techniques [16]. These asymptotic many-particle momentum distributions are determined by the interaction inducing the fragmentation, the bound initial state from which it emerged, and the interactions between the outgoing particles. Thus it is useful to the experimentalist to keep the interaction process as simple as possible and to choose a geometry where final state interactions are negligible or under control. In the present study we used the absorption of a single photon to fragment the deuterium molecule: hν + D 2 → 2 e -+ 2 d + Due to their heavy masses, the initial motion of the nuclei in the continuum can be assumed the same as in the ground state at the instant of the electronic transition (Born Oppenheimer approximation). Once the electrons have left the system, the motion of the nuclei is solely determined by their Coulomb repulsion; they accelerate to a Kinetic Energy Release (KER) which corresponds to the Coulomb potential associated with their initial separation. Quantum mechanically one maps the nuclear vibrational wave-function onto the Coulomb potential to yield a KER spectrum. Inverting this process determines the squared nuclear vibrational wave-function from the measured KER spectrum [17]. Furthermore, by selecting events that occur within a fixed subregion in the KER spectrum, one samples molecules for which the corresponding internuclear distance is defined much more precisely than the full extent of the initial nuclear wave-function. This allows us to show how the electronic continuum momentum distribution depends on the inter-nuclear separation in the molecule and its orientation with respect to the photon polarization. [18,19,20,21]. In brief, inside our momentum spectrometer, a supersonic D 2 -gas jet was crossed with the linear polarized photon beam from the LBNL Advanced Light Source (D 2 provides a higher target density than a comparable H 2 gas jet and data less contaminated by random coincidences from background H 2 O). The electrons and ions created in the intersection of the photons with

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mentioning

confidence: 99%

Complete photo-fragmentation of the deuterium molecule

Weber

Czasch

Jagutzki

et al. 2004

Nature

154

132

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“…One open problem is electron correlation in direct double ionisation of fixed in space H 2 (Kossmann et al 1989;Reddish et al 1997;Dörner et al 1998a;Reddish and Feagin 1998;Feagin 1998;Walter and Briggs 1999;Walter and Briggs 2000). In this case not only the internuclear axis but also the internuclear distance at the instant of photoabsorption can be measured via the ion fragment momenta.…”

Section: Photoionisation Of Fixed-in-space Moleculesmentioning

confidence: 99%

Recoil-ion and electron momentum spectroscopy: reaction-microscopes

et al. 2003

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Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to π Microccopes -the "bubble chambers of atomic physics" -mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields.The present review concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of highintensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using Reaction Microccopes. Third, for electron and ion-impact, the investigation of twoelectron reactions has matured to a state such that first fully differential cross sections (FDCS) are reported. Forth, comprehensive sets of FDCS for single ionisation of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is shortly envisaged.2

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“…Despite this similarity of the PDI of He and H 2 some selection rules that exclude certain escape geometries are relaxed for H 2 ( [9,11]). Primarily, this relaxation stems from the loss of a fixed angular momentum for the photoelectron pair; i.e., the electronic continuum wave function does not have pure P symmetry.…”

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confidence: 99%

“…1 and [1]); thus for He this configuration is doubly forbidden. For H 2 , only the back-to-back emission is forbidden [11]; the rest of the cone is accessible for most molecular orientations. Until recently, this prediction was confirmed only indirectly by coplanar measurements from randomly oriented molecules.…”

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confidence: 99%

Fully Differential Cross Sections for Photo-Double-Ionization ofD2_

et al. 2004

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We report the first kinematically complete study of the four-body fragmentation of the D2 molecule following absorption of a single photon. For equal energy sharing of the two electrons and a photon energy of 75.5 eV, we observed the relaxation of one of the selection rules valid for He photo-double-ionization and a strong dependence of the electron angular distribution on the orientation of the molecular axis. This effect is reproduced by a model in which a pair of photoionization amplitudes is introduced for the light polarization parallel and perpendicular to the molecular axis.

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Selection Rules and Isotope Effects in the Full Fragmentation of the Hydrogen Molecule

Cited by 24 publications

References 8 publications

Complete photo-fragmentation of the deuterium molecule

Complete photo-fragmentation of the deuterium molecule

Recoil-ion and electron momentum spectroscopy: reaction-microscopes

Fully Differential Cross Sections for Photo-Double-Ionization ofD2_

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