High harmonic light sources make it possible to access attosecond timescales, thus opening up the prospect of manipulating electronic wave packets for steering molecular dynamics. However, two decades after the birth of attosecond physics, the concept of attosecond chemistry has not yet been realized; this is because excitation and manipulation of molecular orbitals requires precisely controlled attosecond waveforms in the deep UV, which have not yet been synthesized. Here, we present a unique approach using attosecond vacuum UV pulse-trains to coherently excite and control the outcome of a simple chemical reaction in a deuterium molecule in a non-Born-Oppenheimer regime. By controlling the interfering pathways of electron wave packets in the excited neutral and singly ionized molecule, we unambiguously show that we can switch the excited electronic state on attosecond timescales, coherently guide the nuclear wave packets to dictate the way a neutral molecule vibrates, and steer and manipulate the ionization and dissociation channels. Furthermore, through advanced theory, we succeed in rigorously modeling multiscale electron and nuclear quantum control in a molecule. The observed richness and complexity of the dynamics, even in this very simplest of molecules, is both remarkable and daunting, and presents intriguing new possibilities for bridging the gap between attosecond physics and attochemistry.chemical dynamics | electron dynamics | ultrafast T he coherent manipulation of quantum systems on their natural timescales, as a means to control the evolution of a system, is an important goal for a broad range of science and technology, including chemical dynamics and quantum information science. In molecules, these timescales span from attosecond timescales characteristic of electronic dynamics, to femtosecond timescales characteristic of vibrations and dissociation, to picosecond timescales characteristic of rotations in molecules. With the advent of femtosecond lasers, observing the transition state in a chemical reaction (1), and controlling the reaction itself, became feasible. Precisely timed femtosecond pulse sequences can be used to selectively excite vibrations in a molecule, allow it to evolve, and finally excite or deexcite it into an electronic state not directly accessible from the ground state (2). Alternatively, interferences between different quantum pathways that end up in the same final state can be used to control the outcome of a chemical reaction (3)(4)(5)(6)(7)(8)(9).In recent years, coherent high harmonic sources with bandwidths sufficient to generate either attosecond pulse trains or a single isolated attosecond pulses have been developed that are also perfectly synchronized to the driving femtosecond laser (10-12). This new capability provides intriguing possibilities for coherently and simultaneously controlling both the electronic and nuclear dynamics in a molecule in regimes where the BornOppenheimer approximation is no longer valid, to select specific reaction pathways or products. Here...

We have measured in-plane and out-of-plane diffraction of H2 and D2 molecular beams scattered by reactive Pd(111) and nonreactive NiAl(110) surfaces at 140-150 meV. A comparison with six-dimensional quantum dynamics and classical trajectory calculations shows for the first time that accurate diffraction patterns can be obtained from state-of-the-art potential energy surfaces based on density functional theory. Our measurements show that, at general incidence conditions, out-of-plane diffraction is much more important than was assumed in previous experiments.

We present a theoretical study of H þ 2 ionization under strong IR femtosecond pulses by using a method designed to extract correlated (2D) photoelectron and proton kinetic energy spectra. The results show two distinct ionization mechanisms-tunnel and multiphoton ionization-in which electrons and nuclei do not share the energy from the field in the same way. Electrons produced in multiphoton ionization share part of their energy with the nuclei, an effect that shows up in the 2D spectra in the form of energy-conservation fringes similar to those observed in weak-field ionization of diatomic molecules. In contrast, tunneling electrons lead to fringes whose position does not depend on the proton kinetic energy. At high intensity, the two processes coexist and the 2D plots show a very rich behavior, suggesting that the correlation between electron and nuclear dynamics in strong field ionization is more complex than one would have anticipated. DOI: 10.1103/PhysRevLett.110.113001 PACS numbers: 33.20.Xx, 33.60.+q, 33.80.Rv The interaction of atoms and molecules with intense infrared laser pulses has been the object of continuous research for more than two decades [1][2][3][4][5][6][7][8][9]. Since the potential induced by such lasers on the electrons is comparable to or even stronger than that generated by the nuclei, the resulting electron dynamics is significantly different from that of the isolated system, which makes these lasers ideal tools to achieve electronic control [10][11][12][13]. Strong fields can efficiently excite and ionize atoms and molecules. The electrons, which can be ejected following either multiphoton absorption or tunneling, can either directly reach the detector after having been repeatedly accelerated and decelerated by the field [direct electrons (DE)] or recollide with the ionic core within an optical cycle [rescattered electrons (RE)] [14,15]. Only a small fraction of the ejected electrons rescatter, but this fraction is responsible for important nonlinear phenomena such as high-harmonic generation (HHG). In this process, high-energy photons are emitted as a result of electron recombination with the ionic core. HHG is currently used to produce ultrashort extreme ultraviolet laser pulses and trains of these pulses [16][17][18][19], and also to uncover multielectron dynamics in atoms and molecules [13,20] or the structure of atomic and molecular orbitals in the so-called orbital tomography [10,21,22].Rescattered electrons that do not recombine with the ion also leave their signature in the photoelectron spectra at relatively high energies, typically between 2U p and 10U p [23,24], where U p ¼ I=4! 2 is the electron ponderomotive energy (in a.u.), I is the laser intensity, and ! its frequency. Because of their high energy, in contrast with that of direct electrons which is 2U p , RE can be used as signal and DE as reference to image atomic and molecular structure by photoelectron holography [20,25].Compared to atoms, the study of strong-field electron dynamics in molecules, in particular ...

We present quasiclassical dynamics calculations of H2 and D2 scattering by the NiAl(110) surface using a recently proposed six-dimensional potential-energy surface (PES) obtained from density-functional theory calculations. The results for dissociative adsorption confirm several experimental predictions using (rotationally hot) D2 beams, namely, the existence of a dissociation barrier, the small isotopic effect, the importance of vibrational enhancement, and the existence of normal energy scaling. The latter conclusion shows that normal energy scaling is not necessarily associated with weak corrugated surfaces. The results for rotationally elastic and inelastic diffractions are also in reasonable agreement with experiment, but they show that many more diffractive transitions are responsible for the observed structures than previously assumed. This points to the validity of the PES recently proposed [P. Riviere, H. F. Busnengo, and F. Martin, J. Chem. Phys. 121, 751 (2004)] to describe dissociative adsorption as well as rotationally elastic and inelastic diffractions in the H2NiAl(110) system.

We present an extension of the resolvent-operator method (ROM), originally designed for atomic systems, to extract differential photoelectron spectra (in photoelectron-and nuclear-kinetic energy) for diatomic molecules interacting with strong, ultrashort laser fields in the single active electron approximation. The method is applied to the study of H 2 + photodissociation and photoionization by femtosecond laser pulses in the XUV-IR frequency range. In particular, the method is tested (i) in the perturbative regime, for few-photon absorption and bound-bound electronic transitions, and (ii) in the strong-field regime, in which multiphoton absorption and tunneling are present. In the latter case, we show how the differential ROM allows one to track the transition between both regimes. We also analyze isotopic effects by comparing the dynamics of H 2 + and D 2 + ionization for different pulses.