Controlling Fragmentation of the Acetylene Cation in the Vacuum Ultraviolet via Transient Molecular Alignment.

An open-loop control scheme of molecular fragmentation based on transient molecular alignment combined with single-photon ionization induced by a short-wavelength free electron laser (FEL) is demonstrated for the acetylene cation. Photoelectron spectra are recorded, complementing the ion yield measurements, to demonstrate that such control is the consequence of changes in the electronic response with molecular orientation relative to the ionizing field. We show that stable C2H2+ cations are mainly produced when the molecules are parallel or nearly parallel to the FEL polarization, while the hydrogen fragmentation channel (C2H2+ → C2H+ + H) predominates when the molecule is perpendicular to that direction, thus allowing one to distinguish between the two photochemical processes. The experimental findings are supported by state-of-the art theoretical calculations.

Attention-deficit hyperactivity disorder and executive dysfunction in preschool children. A comparison of NEPSY and BRIEF-P assessments.

OBJECTIVE: The aim of the study was to explore prevalence, interrelations and accuracy of assessing psychopathology, intelligence, and executive functions (EF) in preschool children with ADHD (age 2.1-6.5 years). METHOD: We prospectively investigated 115 preschool outpatient children (91 boys, 24 girls, aged 4.3±1.0 years) with the clinical diagnosis of ADHD. Assessment included clinical history, background, psychosocial problems (CBCL, C-TRF), ADHD (DISYPS external ratings), cognitive performance (WPPSI-III, K-ABC), and executive functions (BRIEF-P, NEPSY). RESULTS: We found a high frequency of dysexecutive problems in up to 64 % in the parental BRIEF-P assessments, up to 62 % in the BRIEF-P teachers' assessments, and 62 % in the NEPSY functional assessments. Parental and teachers' BRIEF-P scores were only correlated in one subscale, inhibition, and NEPSY and BRIEF-P were not correlated at all. It was found that 42.5 % of the children with noticeable findings had agreeing results in all three, and another 45 % in two tests. CONCLUSIONS: About 2/3 of the ADHD preschool children had detectable EF dysfunctions. In order to assess dysexecutive problems, multi-method testing is mandatory.

Absolute timing of the photoelectric effect.

Photoemission spectroscopy is central to understanding the inner workings of condensed matter, from simple metals and semiconductors to complex materials such as Mott insulators and superconductors1. Most state-of-the-art knowledge about such solids stems from spectroscopic investigations, and use of subfemtosecond light pulses can provide a time-domain perspective. For example, attosecond (10-18 seconds) metrology allows electron wave packet creation, transport and scattering to be followed on atomic length scales and on attosecond timescales2-7. However, previous studies could not disclose the duration of these processes, because the arrival time of the photons was not known with attosecond precision. Here we show that this main source of ambiguity can be overcome by introducing the atomic chronoscope method, which references all measured timings to the moment of light-pulse arrival and therefore provides absolute timing of the processes under scrutiny. Our proof-of-principle experiment reveals that photoemission from the tungsten conduction band can proceed faster than previously anticipated. By contrast, the duration of electron emanation from core states is correctly described by semiclassical modelling. These findings highlight the necessity of treating the origin, initial excitation and transport of electrons in advanced modelling of the attosecond response of solids, and our absolute data provide a benchmark. Starting from a robustly characterized surface, we then extend attosecond spectroscopy towards isolating the emission properties of atomic adsorbates on surfaces and demonstrate that these act as photoemitters with instantaneous response. We also find that the tungsten core-electron timing remains unchanged by the adsorption of less than one monolayer of dielectric atoms, providing a starting point for the exploration of excitation and charge migration in technologically and biologically relevant adsorbate systems.