Atomic autoionization in the photo-dissociation of super-excited deuterated water molecules fragmenting into D+ + O+ + D.

We present the relaxation dynamics of deuterated water molecules via autoionization, initiated by the absorption of a 61 eV photon, producing the very rare D+ + O+ + D breakup channel. We employ the COLd target recoil ion momentum spectroscopy method to measure the 3D momenta of the ionic fragments and emitted electrons from the dissociating molecule in coincidence. We interpret the results using the potential energy surfaces extracted from multi-reference configuration interaction calculations. The measured particle energy distributions can be related to a super-excited monocationic state located above the double ionization threshold of D2O. The autoionized electron energy shows a sharp distribution centered around 0.5 eV, which is a signature of the atomic oxygen autoionization occurring in the direct and sequential dissociation processes of D2O+* at a large internuclear distance. In this way, an O+ radical fragment and a low-energy electron are created, both of which can trigger secondary reactions in their environment.

Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O.

We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path-OD+: a1Δ or b1Σ+ → A 3Π â†’ X 3Σ- → B 3Σ--involving a combination of spin-orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels.

Investigating charge-up and fragmentation dynamics of oxygen molecules after interaction with strong X-ray free-electron laser pulses.

During the last decade, X-ray free-electron lasers (XFELs) have enabled the study of light-matter interaction under extreme conditions. Atoms which are subject to XFEL radiation are charged by a complex interplay of (several subsequent) photoionization events and electronic decay processes within a few femtoseconds. The interaction with molecules is even more intriguing, since intricate nuclear dynamics occur as the molecules start to dissociate during the charge-up process. Here, we demonstrate that by analyzing photoelectron angular emission distributions and kinetic energy release of charge states of ionic molecular fragments, we can obtain a detailed understanding of the charge-up and fragmentation dynamics. Our novel approach allows for gathering such information without the need of complex ab initio modeling. As an example, we provide a detailed view on the processes happening on a femtosecond time scale in oxygen molecules exposed to intense XFEL pulses.

Selective bond-breaking in formic acid by dissociative electron attachment.

We report the results of a joint experimental and theoretical study of dissociative electron attachment to formic acid (HCOOH) in the 6-9 eV region, where H- fragment ions are a dominant product. Breaking of the C-H and O-H bonds is distinguished experimentally by deuteration of either site. We show that in this region H- ions can be produced by formation of two or possibly three Feshbach resonance (doubly-excited anion) states, one of which leads to either C-H or O-H bond scission, while the other can only produce formyloxyl radicals by O-H bond scission. Comparison of experimental and theoretical angular distributions of the anion fragment allows the elucidation of state specific pathways to dissociation.

Resonant Auger decay driving intermolecular Coulombic decay in molecular dimers.

In 1997, it was predicted that an electronically excited atom or molecule placed in a loosely bound chemical system (such as a hydrogen-bonded or van-der-Waals-bonded cluster) could efficiently decay by transferring its excess energy to a neighbouring species that would then emit a low-energy electron. This intermolecular Coulombic decay (ICD) process has since been shown to be a common phenomenon, raising questions about its role in DNA damage induced by ionizing radiation, in which low-energy electrons are known to play an important part. It was recently suggested that ICD can be triggered efficiently and site-selectively by resonantly core-exciting a target atom, which then transforms through Auger decay into an ionic species with sufficiently high excitation energy to permit ICD to occur. Here we show experimentally that resonant Auger decay can indeed trigger ICD in dimers of both molecular nitrogen and carbon monoxide. By using ion and electron momentum spectroscopy to measure simultaneously the charged species created in the resonant-Auger-driven ICD cascade, we find that ICD occurs in less time than the 20 femtoseconds it would take for individual molecules to undergo dissociation. Our experimental confirmation of this process and its efficiency may trigger renewed efforts to develop resonant X-ray excitation schemes for more localized and targeted cancer radiation therapy.

Resonance signatures in the body-frame valence photoionization of CF4.

We present a combined experimental and theoretical investigation of the electron dynamics and body-frame angular dependence of valence photo-single ionization of CF4 and subsequent dissociation into CF3+ and F. Ionization from a valence t2 orbital shows overlapping shape resonances close to threshold that couple to the same total symmetry, leading to striking changes in the photoelectron angular distributions when viewed in the body-frame.

Pilot Study of Endothelin Receptor Blockade in Heart Failure with Diastolic Dysfunction and Pulmonary Hypertension (BADDHY-Trial).

BACKGROUND: In this multi-centre, randomised, placebo-controlled pilot trial, we investigated the clinical and haemodynamic effects of the endothelin-receptor blocker Bosentan in patients with heart failure, preserved ejection fraction and pulmonary hypertension (PH-HFpEF). MATERIALS AND METHODS: Eligible patients received either 12 weeks of Bosentan therapy, or a placebo drug. Patients were thereafter followed for a further period of 12 weeks without the study medication. At three points during the study (study Commencement, Week 12 and Week 24), a six-minute walk test (6MWT), echocardiographic and laboratory assessments were performed, as well as a quality of life survey. Right heart catheterisation (RHC) was undertaken at commencement only. The study was aborted early, after an interim analysis favoured the placebo. RESULTS: Six-minute walk distance (6MWD) did not change in the Bosentan group (309.7±96.3m (Commencement), 317.0±126.1m (Week 12), 307.0±84.4m (Week 24); p=0.86), but almost reached statistical significance in the placebo group from 328.8±79.6m, to 361.6±98.2m and 384.0±74.9m (Week 24); p=0.075. In the placebo group, estimated systolic pulmonary artery pressure (measured via echocardiography) significantly decreased (from 62.3±16.7mmHg [Commencement], 45.3±13.9mmHg [Week 12], to 44.6±14.5mmHg [Week 24]; p=0.014) as did right atrial pressure (13.1±5.3 [Commencement], 10.0±3.8 [Week 12], to 9.4±3.2 [Week 24]; p=0.046). CONCLUSION: Despite this study's limited sample size and premature cessation, it nevertheless suggests that endothelin receptor blockade in patients with PH-HFpEF may have no beneficial effects and could even be detrimental in comparison to a placebo.

Ejection of quasi-free-electron pairs from the helium-atom ground state by single-photon absorption.

We investigate the single-photon double ionization of helium at photon energies of 440 and 800 eV. We observe doubly charged ions with close to zero momentum corresponding to electrons emitted back to back with equal energy. These slow ions are the unique fingerprint of an elusive quasifree photon double ionization mechanism predicted by Amusia et al. nearly four decades ago [J. Phys. B 8, 1248 (1975)]. It results from the nondipole part of the electromagnetic interaction. Our experimental data are supported by calculations performed using the convergent close-coupling and time-dependent close-coupling methods.

Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser.

Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H2O2+, D2O2+, and HDO2+, such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.

Imaging polyatomic molecules in three dimensions using molecular frame photoelectron angular distributions.

We demonstrate a method for determining the full three-dimensional molecular-frame photoelectron angular distribution in polyatomic molecules using methane as a prototype. Simultaneous double Auger decay and subsequent dissociation allow measurement of the initial momentum vectors of the ionic fragments and the photoelectron in coincidence, allowing full orientation by observing a three-ion decay pathway, (H+, H+, CH2(+)). We find the striking result that at low photoelectron energies the molecule is effectively imaged by the focusing of photoelectrons along bond directions.

Electron diffraction self-imaging of molecular fragmentation in two-step double ionization of water.

We doubly ionize H(2)O by single photon absorption at 43 eV leading to H(+) + OH(+). A direct double ionization and a sequential process in which single ionization is followed by rapid dissociation into a proton and an autoionizing OH(*) are identified. The angular distribution of this delayed autoionization electron shows a preferred emission in the direction of the emitted proton. From this diffraction feature we obtain internuclear distances of 700 to 1100 a.u. at which the autoionization of the OH(*) occurs. The experimental findings are in line with calculations of the excited potential energy surfaces and their lifetimes.

Time resolved 3D momentum imaging of ultrafast dynamics by coherent VUV-XUV radiation.

We present a new experimental setup for measuring ultrafast nuclear and electron dynamics of molecules after photo-excitation and ionization. We combine a high flux femtosecond vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) source with an internally cold molecular beam and a 3D momentum imaging particle spectrometer to measure electrons and ions in coincidence. We describe a variety of tools developed to perform pump-probe studies in the VUV-XUV spectrum and to modify and characterize the photon beam. First benchmark experiments are presented to demonstrate the capabilities of the system.

[The Transplantation Law of October 8, 2004]. / Das Transplantationsgesetz vom 8. Oktober 2004.

The Transplantation Law was approved by Parliament on 8 October 2004. Its key features are a ban on trade in human organs, tissue and cells; the non-entitlement of donors of their next of kin to payment for organs; the definition of when death is considered to have occurred; the need for consent before removal takes place; the criteria for donations by living persons; the criteria and procedure for assigning donated organs to recipients; xenotransplantation; and the transplantation of human embryonic and fetal tissue and cells. As things stand at present, the law is expected to take effect at the beginning of 2007. The current fragmented legislation on transplant medicine will therefore be replaced in two years' time by a modern, consistent and comprehensive legal framework.

Dynamics of the Dissociating Uracil Anion Following Resonant Electron Attachment.

We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3-dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.

Angular correlation between photoelectrons and auger electrons from K-shell ionization of neon.

We have used cold target recoil ion momentum spectroscopy to study the continuum correlation between the photoelectron of core-photoionized neon and the subsequent Auger electron. We observe a strong angular correlation between the two electrons. Classical trajectory Monte Carlo calculations agree quite well with the photoelectron energy distribution that is shifted due to the potential change associated with Auger decay. However, a striking discrepancy results in the distribution of the relative angle between Auger and photoelectron. The classical model predicts a shift in photoelectron flux away from the Auger emission direction, and the data strikingly reveal that the flux is lost rather than diverted, indicating that the two-step interpretation of photoionization followed by Auger emission is insufficient to fully describe the core-photoionization process.

Photo- and auger-electron recoil induced dynamics of interatomic Coulombic decay.

At photon energies near the Ne K edge it is shown that for 1s ionization the Auger electron, and for 2s ionization the fast photoelectron, launch vibrational wave packets in a Ne dimer. These wave packets then decay by emission of a slow electron via interatomic Coulombic decay (ICD). The measured and computed ICD electron spectra are shown to be significantly modified by the recoil induced nuclear motion.

Ultrafast probing of core hole localization in N2.

Although valence electrons are clearly delocalized in molecular bonding frameworks, chemists and physicists have long debated the question of whether the core vacancy created in a homonuclear diatomic molecule by absorption of a single x-ray photon is localized on one atom or delocalized over both. We have been able to clarify this question with an experiment that uses Auger electron angular emission patterns from molecular nitrogen after inner-shell ionization as an ultrafast probe of hole localization. The experiment, along with the accompanying theory, shows that observation of symmetry breaking (localization) or preservation (delocalization) depends on how the quantum entangled Bell state created by Auger decay is detected by the measurement.

Interference in the collective electron momentum in double photoionization of H2.

We investigate single-photon double ionization of H(2) by 130 to 240 eV circularly polarized photons. We find a double slitlike interference pattern in the sum momentum of both electrons in the molecular frame which survives integration over all other degrees of freedom. The difference momentum and the individual electron momentum distributions do not show such a robust interference pattern. We show that this interference results from a non-Heitler-London fraction of the H(2) ground state where both electrons are at the same atomic center.

Binary and recoil collisions in strong field double ionization of helium.

We have investigated the correlated momentum distribution of both electrons from nonsequential double ionization of helium in a 800 nm, 4.5 x 10(14 W/cm2 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.

Single photon-induced symmetry breaking of H2 dissociation.

H2, the smallest and most abundant molecule in the universe, has a perfectly symmetric ground state. What does it take to break this symmetry? We found that the inversion symmetry can be broken by absorption of a linearly polarized photon, which itself has inversion symmetry. In particular, the emission of a photoelectron with subsequent dissociation of the remaining H+2 fragment shows no symmetry with respect to the ionic H+ and neutral H atomic fragments. This lack of symmetry results from the entanglement between symmetric and antisymmetric H+2 states that is caused by autoionization. The mechanisms behind this symmetry breaking are general for all molecules.