Interdependence of ICD Rates in Paired Quantum Dots on Geometry

Using state of the art antisymmetrized multiconfiguration time dependent Hartree MCTDH electron dynamics calculations we study the interdependence of the intermolecular Coulombic decay ICD process on the geometric parameters of a doubly charged paired quantum dot PQD model system in the framework of the effective mass approximation EMA . We find that ICD displays a maximum rate for a certain geometry of the electron emitting quantum dot, which is simultaneously dependent on both the distance between the quantum dots as well as the photon absorbing quantum dot s geometry. The rate maximum is shown to be caused by the competing effects of polarization of electron density and Coulomb repulsion. The ICD rate maximized PQD geometry in GaAs QDs yields a decay time of 102.39 ps. It is given by two vertically aligned cylindrical QDs with radii of 14.42 nm separated by 86.62 nm. The photon absorbing QD then has a height of 46.59 nm and the electron emitting QD a height of 16.33 n

Strong Field Control of the Interatomic Coulombic Decay Process in Quantum Dots

In recent years the laser induced interatomic Coulombic decay ICD process in paired quantum dots has been predicted [J. Chem. Phys. 138 2013 214104]. In this work we target the enhancement of ICD by scanning over a range of strong field laser intensities. The GaAs quantum dots are modeled by a one dimensional double well potential in which simulations are done with the space resolved multi configuration time dependent Hartree method including antisymmetrization to account for the fermions. As a novelty a complementary state resolved ansatz is developed to consolidate the interpretation of transient state populations, widths obtained for the ICD and the competing direct ionization channel, and Fano peak profiles in the photoelectron spectra. The major results are that multi photon processes are unimportant even for the strongest fields. Further, below pi to pi pulses display the highest ICD efficiency while the direct ionization becomes less dominan

Isomeric Xylene Molecules in the Terahertz Far Infrared Regime Computational Chemistry and Spectral Modeling View

The theoretical assignments of spectral peaks of liquid phase ortho , meta , and para xylene recorded with far infrared FIR and THz spectroscopy in the spectral range between 550 and 50 cm amp; 8722;1 is done with density functional theory DFT calculations. As THz spectroscopic techniques drastically evolved in recent years, the critical focus of this paper lies on the applicability of theoretical concepts, used as computational standard in near and mid IR spectra, to the FIR THz region. An evaluation of the choice of functionals, basis sets, and appropriate scaling factors as well as the tractability of the liquid phase in a polarizable continuum model is performed. Alongside a new analysis procedure based on spectral Hard Modeling has been developed. DFT line spectra are fitted to experimental FIR spectra where a quantitative track record allows for meaningful comparisons. With all these tools we are able to reproduce experimental spectra in an optically appealing way and we can explain trends for each spectrum as well as across the row of the isomer

Fourier Spektroskopische Untersuchungen im Mittleren und Fernen Infrarotbereich an Co 60 bestrahlten und thermisch belasteten ultrahochmolekularen Polyethylen Proben

Fourier Spektroskopische Untersuchungen von hochmolekularem Polyethylen HMW PE und ultrahochmolekularem Polyethylen UHMW PE im Mittleren und Fernen Infrarotbereich können Veränderungen der molekularen Strukturen nachweisen, die durch Co60 amp; 947; Strahlung und Rekristallisationsprozesse initiiert werden. UHMW PE und HMW PE sind im gewählten IR Bereich unterscheidbar. Die integrale Absorption der B1u Gitterschwingungen im Fernen Infrarotbereich THz Bereich ermöglichen die quantitative Beschreibung des Kristallinitätsgrades und dessen Abbau. Die Bildung ungesättigter Vinylengruppen und der Abbau ungesättigter Methylengruppen können im Mittleren Infrarotbereich nachgewiesen werde

THz and mid IR Fourier Transform Spectroscopy on Polyethylene irradiated with gamma Co60 radiation

THz and mid IR spectroscopy of high molecular PE HMW and ultra high molecular PE UHMW reveals modifications of the molecular structure induced by amp; 947; Co60 radiation. UHMW PE and HMW PE can be distinguished. The integral absorption in the B1u THz region can quantitatively describe the amorphization of crystallinity. The formation of trans vinylene unsaturations and the decay of vinyl can be followed by mid IR spectroscop

Introducing Ionic Current Detection for X Ray Absorption Spectroscopy in Liquid Cells

Photons and electrons are two common relaxation products upon X ray absorption, enabling fluorescence yield and electron yield detections for X ray absorption spectroscopy XAS . The ions that are created during the electron yield process are relaxation products too, which are exploited in this study to produce ion yield for XA detection. The ionic currents measured in a liquid cell filled with water or iron III nitrate aqueous solutions exhibit characteristic O K edge and Fe L edge absorption profiles as a function of excitation energy. Application of two electrodes installed in the cell is crucial for obtaining the XA spectra of the liquids behind membranes. Using a single electrode can only probe the species adsorbed on the membrane surface. The ionic current detection, termed as total ion yield TIY in this study, also produces an undistorted Fe L edge XA spectrum, indicating its promising role as a novel detection method for XAS studies in liquid cell

Injection Kinetics and Electronic Structure at the N719 TiO2 Interface Studied by Means of Ultrafast XUV Photoemission Spectroscopy

The method of transient XUV photoemission spectroscopy is developed to investigate the ultrafast dynamics of heterogeneous electron transfer at the interface between the N719 ruthenium dye complex and TiO2 nanoparticles. XUV light from high order harmonic generation is used to probe the electron density distribution among the ground and excited states at the interface after its exposure to a pump laser pulse of 530 nm wavelength. A spectral decomposition of the transient emission signal is used to follow the population and decay dynamics of the involved transient states individually. By comparing results obtained for the N719 TiO2 and N719 FTO interfaces, we can unambiguously reveal the kinetics of electrons injected to TiO2 from the singlet metal to ligand charge transfer MLCT excited state of the dye. With the developed approach, we characterize both the kinetic constants and the absolute binding energies of the singlet and triplet MLCT states of the dye and the state of electrons injected to the conduction band of TiO2. The energy levels of the singlet and triplet states are found to lie 0.7 eV above and 0.2 eV below the conduction band minimum, respectively. This energetic structure gives rise to a strong driving force for injection from the singlet state and a slow electron transfer from the triplet state, the latter being possible due to a partial overlap of the triplet state band of N719 and the conduction band of TiO

Aqueous Solution Chemistry of Ammonium Cation in the Auger Time Window

We report on chemical reactions triggered by core level ionization of ammonium NH4 cation in aqueous solution. Based on a combination of photoemission experiments from a liquid microjet combined with high level ab initio simulations, we identified simultaneous single and double proton transfer occurring on a very short time scale spanned by the Auger decay lifetime. Molecular dynamics simulations indicate that the proton transfer to a neighboring water molecule leads to essentially complete formation of H3O aq and core ionized ammonia NH3 amp; 8270; aq within the 7 fs lifetime of the nitrogen 1s core hole. A second proton transfer leads to a transient structure with the proton shared between the remaining NH2 moiety and another water molecule in the hydration shell. These ultrafast proton transfers are stimulated by very strong hydrogen bonds between the ammonium cation and water. Experimentally, the proton transfer dynamics is identified from an emerging signal at the highkinetic energy side of the Auger electron spectrum in analogy to observations made for other hydrogenbonded aqueous solutions. The present study represents the most pronounced charge separation observed upon core ionization in liquids so fa

Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates

We report on a newly built laser based tabletop setup which enables generation of femtosecond light pulses in the XUV range via employing the process of high order harmonic generation HHG in a gas medium. The spatial, spectral, and temporal characteristics of the XUV beam are presented. Monochromatization of XUV light with minimum temporal pulse distortion is the central issue of this work. Off center reflection zone plates are shown to be superior to gratings when selection of a desired harmonic is carried out with the use of a single optical element. A cross correlation technique was applied to characterize the performance of zone plates in the time domain. By using laser pulses of 25 fs length to pump the HHG process, a pulse duration of 45 fs for monochromatized harmonics was achieved in the present setu

Local electronic structure of aqueous zinc acetate oxygen K edge X ray absorption and emission spectroscopy on micro jets

Oxygen K edge X ray absorption, emission, and resonant inelastic X ray scattering spectra were measured to site selectively gain insights into the electronic structure of aqueous zinc acetate solution. The character of the acetate ion and the influence of zinc and water on its local electronic structure are discusse