We study dissociative photoionization of molecular oxygen in a kinematically complete XUV-IR pump-probe experiment. Detecting charged fragments and photoelectrons in coincidence using a reaction microscope, we observe a pump-probe delay-dependent yield of very low energetic O + ions which oscillates with a period of 40 fs. This feature is caused by a time-dependent vibrational wave packet in the potential of the binding O 2 + (a 4 u ) state, which is probed by resonant absorption of a single infrared photon to the weakly repulsive O 2 + (f 4 g ) state. By quantitative comparison of the experimental kinetic-energy-release (KER) and quantum-beat (QB) spectra with the results of a coupled-channel simulation, we are able to discriminate between the calculated adiabatic O + 2 potential-energy curves ( (2012)]. In general, we find a good agreement between experimental and simulated KER and QB spectra. However, we could not reproduce all features of the experimental data with these PECs. In contrast, adjusting a Morse potential to the experimental data, most features of the experimental spectra are well reproduced by our simulation. By comparing this Morse potential to theoretically predicted PECs, we demonstrate the sensitivity of our experimental method to small changes in the shape of the binding potential.

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...

The ultrafast transfer of excitation energy from one atom to its neighbor is observed in singly charged argon dimers in a time-resolved extreme ultraviolet (XUV)-pump IR-probe experiment. In the pump step, bound 3s-hole states in the dimer are populated by single XUV-photon ionization. The excitation-energy transfer at avoided crossings of the potential-energy curves leads to dissociation of the dimer, which is experimentally observed by further ionization with a time-delayed IR-probe pulse. From the measured pump-probe delay-dependent kinetic-energy release of coincident Ar + Ar ions, we conclude that the transfer of energy occurs on a time scale of about 800fs. This mechanism represents a fast relaxation process below the energy threshold for interatomic Coulombic decay.

We present a kinematically complete and time-resolved study of the dissociation dynamics of H 2 + using ultrashort extreme-ultraviolet and near-infrared laser pulses. The reaction kinematics can be controlled by varying the time delay between the two pulses. We demonstrate that a time-dependent laser-dressed potential-energy curve enables the control of the nuclear motion. The dynamics is well reproduced by intuitive semiclassical trajectories on a time-dependent potential curve. From this most fundamental scenario we gain insight in the underlying mechanisms which may be applied as design principles for molecular quantum control, particularly for ultrafast molecular reactions involving the motion of protons

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