Molecular structure is usually determined by measuring the diffraction pattern the molecule impresses on x-rays or electrons. We used a laser field to extract electrons from the molecule itself, accelerate them, and in some cases force them to recollide with and diffract from the parent ion, all within a fraction of a laser period. Here, we show that the momentum distribution of the extracted electron carries the fingerprint of the highest occupied molecular orbital, whereas the elastically scattered electrons reveal the position of the nuclear components of the molecule. Thus, in one comprehensive technology, the photoelectrons give detailed information about the electronic orbital and the position of the nuclei.

At the transition from the gas to the liquid phase of water, a wealth of new phenomena emerge, which are absent for isolated H 2 O molecules. Many of those are important for the existence of life, for astrophysics and atmospheric science. In particular, the response to electronic excitation changes completely as more degrees of freedom become available. Here we report the direct observation of an ultrafast transfer of energy across the hydrogen bridge in (H 2 O) 2 (a so-called water dimer). This intermolecular coulombic decay leads to an ejection of a low-energy electron from the molecular neighbour of the initially excited molecule. We observe that this decay is faster than the proton transfer that is usually a prominent pathway in the case of electronic excitation of small water clusters and leads to dissociation of the water dimer into two H 2 O , the observed decay channel might contribute as a source of electrons that can cause radiation damage in biological matter.The water molecule is, as a triatomic molecule, rather simple in structure and its geometry is well known. In contrast to that, the interplay of compounds of water molecules or other atoms and molecules with water, for example in a solution, is very rich and far from being fully understood. At the very onset of condensation when two water molecules are combined to form a water dimer a new dimension of complexity arises: electronic excitation of this complex spawns nuclear dynamics leading to fragmentation into a protonated fragment (that is, H 3 O + ) and an OH group 3,4 . For this fragmentation, first a proton migrates from one of the molecules to its neighbour, usually along a distance that is larger than the bond lengths found in the water molecule itself. Such fragmentation dynamics are characteristic for larger clusters, as well 5 . Typical mass spectra of fragments of water droplets show a break-up into protonated cluster fragments (H 2 O) n H + of different sizes and into OH groups. A reason for this is the absence of direct transitions within the Franck-Condon region to break-up channels that do not involve proton migration [6][7][8] . Furthermore, the migration itself is highly efficient and occurs on a timescale of <60 fs (ref. 9).The response of condensed water to electronic excitation has far-reaching consequences for biological systems. Radiation damage to cells naturally depends sensitively on the routes by which energy deposited into the cells is finally distributed and which fragmentation and de-excitation pathways are favoured. Experiments have shown that the constituents of DNA are highly vulnerable to low-energy electrons 1 . These studies revealed that not only does primary ionization by high-energy particles or photons cause damage, but also that low-energy electrons in particular break-up biomolecules efficiently 2 . ). The red oval shows an internuclear distance of 2.9 Å with a corresponding KER of 4.9 eV after the photo reaction. b,c, The process observed in this experiment: an electron from the inner valence shell of one...

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Binary and recoil collisions in strong field double ionization of helium Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1103/PhysRevLett.99.263002Physical Review Letters, 99, 26, 2007 We have investigated the correlated momentum distribution of both electrons from nonsequential double ionization of helium in a 800 nm, 4:5 10 14 W=cm 2 laser field. Using very high resolution coincidence techniques, we find a so-far unobserved fingerlike structure in the correlated electron momentum distribution. The structure can be interpreted as a signature of the microscopic dynamics in the recollision process. We identify features corresponding to the binary and recoil lobe in field-free (e; 2e) collisions. This interpretation is supported by analyzing ab initio solutions of a fully correlated three-dimensional helium model. Binary and Recoil Collisions in Strong Field Double Ionization of Helium

We coincidently measure the molecular-frame photoelectron angular distribution and the ion sum-momentum distribution of single and double ionization of CO molecules by using circularly and elliptically polarized femtosecond laser pulses, respectively. The orientation dependent ionization rates for various kinetic energy releases allow us to individually identify the ionizations of multiple orbitals, ranging from the highest occupied to the next two lower-lying molecular orbitals for various channels observed in our experiments. Not only the emission of a single electron, but also the sequential tunneling dynamics of two electrons from multiple orbitals are traced step by step. Our results confirm that the shape of the ionizing orbitals determine the strong laser field tunneling ionization in the CO molecule, whereas the linear Stark effect plays a minor role.

Laser-driven electron recollision is at the heart of the rapidly growing field of attosecond science. The recollision wavepacket is qualitatively described within the strong-field approximation, which commonly assumes tunnelling ionization and plane-wave propagation of the liberated electron in the continuum. However, with increasing experimental sophistication, refinements to this simple model have become necessary. Through careful modelling and measurements of laser-induced recollision holography using aligned N 2 molecules, we demonstrate that the continuum electron wavepacket already carries a non-trivial spatial phase structure immediately following ionization. This e ect is of rather general character: any molecule and any non-isotropic system that is ionized by a strong laser field will exhibit an o set in the phase of the continuum electron wavepacket. Specifically, this has important implications for any coherent scattering process in molecules, such as highharmonic generation or laser-induced electron holography.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Attosecond strobing of two-surface population dynamics in dissociating H₂+ NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21276171&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21276171&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions?Contact the NRC Publications Archive team at PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1103/PhysRevLett.98.073003Physical Review Letters, 98, 7, 2007-02-14 The interplay of population between two isolated electronic levels is the major tool in quantum optics and molecular science. In molecular science, controlling electronic excitation controls the bond. This is used to make cold molecules from cold atoms (e.g., [1]). It is also used to break symmetry in molecules [2,3]. Even nonresonant population transfer can control reaction pathways [4].We report the observation of electronic population dynamics -as it occurs. As illustrated in Fig. 1, we use the ground (1s g ) and first excited states (2p u )ofH 2 as our two-level system. The 1s g and 2p u states are isolated from all other electronic levels, dipole coupled, and degenerate in the separated atom limit. Experimentally, we prepare the H 2 by ionizing H 2 in an intense infrared laser pulse. Components of the vibrational wave packet created by tunnel ionization can sweep through both the one-and three-photon resonances between the two surfaces. Population is transferred from 1s g to 2p u via adiabatic rapid passage (the general term given to these processes in quantum optics) or bond softening (the term used in strong field molecular physics) [5,6]. In our experiment, which uses near infrared light, a snapshot of the upper state population is taken within a time window of a few hundred attoseconds via Coulomb explosion imaging. This snapshot is repeated every half las...

molecules show a much increased multiple ionization rate in a strong laser field as compared with atoms of similar ionization energy. A widely accepted model attributes this to the action of the joint fields of the adjacent ionic core and the laser on its neighbour inside the same molecule. The underlying physical picture for the enhanced ionization is that it is the up-field atom that gets ionized. However, this is still debated and remains unproven. Here we report an experimental verification of this long-standing prediction. This is accomplished by probing the two-site double ionization of ArXe, where the instantaneous field direction at the moment of electron release and the emission direction of the correlated ionizing centre are measured by detecting the recoil sum-and relative-momenta of the fragment ions. our results unambiguously prove the intuitive picture of the enhanced multielectron dissociative ionization of molecules and clarify a long-standing controversy.

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