Electron Localization Involving Doubly Excited States in Broadband Extreme Ultraviolet Ionization ofH2

Abstract

Dissociative single ionization of H 2 induced by extreme ultraviolet photons from an attosecond pulse train has been studied in a kinematically complete experiment. Depending on the electron kinetic energy and the alignment of the molecule with respect to the laser polarization axis, we observe pronounced asymmetries in the relative emission directions of the photoelectron and the H þ ion. The energydependent asymmetry pattern is explained by a semiclassical model and further validated by fully quantum mechanical calculations, both in very good agreement with the experiment. DOI: 10.1103/PhysRevLett.110.213002 PACS numbers: 33.80.Eh Molecular hydrogen is the simplest molecule that exhibits electron correlation and doubly excited states. Having a total energy above the ionization threshold, they are embedded in the single-ionization continuum and thus autoionize via emission of an electron on a time scale that is comparable to the dissociation time. The dynamical interplay between the electronic and nuclear motion in autoionization has been the subject of research [1,2]. It has raised particular attention with the advent of ultrashort light pulses whose durations may permit real-time imaging and control of these processes [3].Theoretical investigations suggested that the symmetry of hydrogenic molecules (H 2 , D 2 , HD) can be broken after light-induced ionization [4][5][6]. This is a consequence of interferences arising from a coherent superposition of ionic molecular states with different parities resulting in the localization of the remaining bound electron. Several experiments demonstrated this for multiphoton processes [3,[7][8][9][10] as well as for single-photon transitions [6,11,12]. However, a fully differential analysis of the asymmetry arising from electron localization in photoionization induced by spectrally broad laser pulses has never been reported.Here, we present experimental data on H 2 photoionization using an attosecond pulse train. Using a semiclassical model [13][14][15] based on the WKB approximation, we demonstrate that both the origin of the observed asymmetry and its oscillations as a function of the kinetic energies of the charged fragments can be accounted for fully. The present findings are further confirmed by a fully quantum mechanical calculation.In the experiment ð35 AE 10Þ fs IR pulses, provided by a commercial laser system, are spectrally broadened in a hollow core fiber and recompressed to ð15 AE 5Þ fs using chirped mirrors. Using high harmonic generation [16] in argon followed by an aluminum filter to remove the fundamental light, we reach extreme ultraviolet (XUV) photon energies between 16 and 37 eV. The high harmonics are emitted as attosecond pulse trains where the number of pulses depends on the duration of the generating laser pulse and is here estimated to be less than 10. The XUV beam is then focused into a supersonic jet of hydrogen gas. The focal spot is placed in the center of a reaction microscope [17] enabling the measurement of the individual momenta of all c...

Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

“…Recent studies showed how femtosecond VUV and XUV radiation can be used to reveal transient nuclear and electron dynamics in diatomic molecules [8][9][10][11][12] as well as in more complex molecular systems [13,14]. To probe such dynamics, the majority of the pump-probe-style experiments accomplished to date utilize not only pairs of XUV-IR pulses [8,[15][16][17][18], but also a combination of VUV-XUV pulses [19][20][21][22]. These experiments have led to the observation of novel ultrafast phenomena in molecules and have allowed for the temporal characterization of known dissociation processes [21].…”

Coherent Electron Hole Dynamics Near a Conical Intersection

“…On the other hand, time-domain studies can elucidate the dynamic nature of correlations driving ultrafast charge dynamics in molecules and can open the door for the direct control of reaction pathways. Attosecond and femtosecond XUV pulses based on nonlinear high-harmonic generation (HHG) offer sufficiently broad bandwidths, forming an ideal tool for probing electronic superpositions in a wide variety of systems [5,6,11,12]. However, these techniques have not been applied in the pump-probe studies of coherent charge dynamics in polyatomic systems that exhibit complex behavior near conical intersections.…”

“…Therefore, the natural time scale for charge motion lies in the attosecond to femtosecond regime. Recent developments in attosecond, extreme ultraviolet (XUV) science provide new opportunities for the real-time investigation of electron dynamics in atomic [3][4][5][6] and molecular systems [7][8][9][10][11][12][13]. Specifically, by virtue of the high photon energy, ultrafast XUV pulses allow access to electron hole dynamics in photoionized molecules, an unexplored class of charge transfer phenomena [14][15][16].…”

Revealing the role of electron-electron correlations by mapping dissociation of highly excited D2+ using ultrashort XUV pulses

“…Write Attention: PRA Project Manager and the Article ID, XH10238A, on the proof copy unless it is already printed on your proof printout. by steering the reaction with unprecedented precision [19][20][21][22][23].…”