High-energy Photoelectron Spectra Research Articles

Dependence of the returning electron wave packet on the model potential for high-energy plateau photoelectron spectra

SynopsisIn the present work, we study the two-dimensional momentum distributions of high-energy plateau photoelectrons of a model-atom in a linearly polarized few-cycle laser pulse. Based on the improved strong-field approximation (ISFA), it is found that the returning electron wave packet is dependent of the model potential.

Tomographic Extraction of the Internuclear Separation Based on Two-Center Interference with Aligned Diatomic Molecules.

We experimentally investigate the two-dimensional photoelectron momentum spectra of aligned diatomic molecules in an intense laser field. Our results reveal a novel prominent valley structure in the molecular alignment dependence of the high-energy photoelectron spectra along the laser polarization. Resorting to the molecular strong-field approximation and a simple semiclassical analysis, we show that this valley structure stems from the destructive two-center interference of the laser-driven rescattered electrons in diatomic molecules. Based on this two-center interference with aligned diatomic molecules, we demonstrate for the first time a tomographic method to extract the molecular internuclear separation, providing a more straightforward approach of molecular imaging, in comparison with, e.g., laser-induced electron diffraction and fixed-angle broadband laser-driven electron scattering.

Retrieval of parameters of few-cycle laser pulses from high-energy photoelectron spectra of atoms by a genetic algorithm

Retrieval of parameters of few-cycle laser pulses from high-energy photoelectron spectra of atoms by a genetic algorithm

Validity of the quantitative rescattering model for two-color strong laser pulses

Recently, we have developed a quantitative rescattering (QRS) model for linearly polarized laser pulses. According to the QRS model, the yield of the high-energy photoelectron spectra can be expressed as a product of the returning electron wave packet and the elastic differential cross section for free electrons scattered with the parent ion. In this paper, the QRS model is applied to the case of two-color strong laser pulses. The validity of the QRS model for two-color pulses is examined by comparing the high-energy photoelectron spectra simulated from the QRS model with the results from solving the time-dependent Schrödinger equation.

Elastic scattering and impact ionization by returning electrons induced in a strong laser field

We study elastic scattering and impact ionization by returning electrons induced in a strong laser field based on the recently developed quantitative rescattering theory. The high-energy angle-resolved photoelectron spectra of molecules in strong fields are attributed to elastic scattering of the returning electrons with the parent ion. We demonstrate that the high-energy photoelectron spectra can be used to retrieve the position of atoms in a molecule. We also investigate the nonsequential double ionization of an atom in intense laser fields which is partly due to the impact ionization of the parent ion by the returning electron.

Self-imaging of molecules from diffraction spectra by laser-induced rescattering electrons

We study high-energy angle-resolved photoelectron spectra of molecules in strong fields. In an oscillating laser electric field, electrons released earlier in the pulse may return to recollide with the target ion, in a process similar to scattering by laboratory prepared electrons. If midinfrared lasers are used, we show that the images generated by the returning electrons are similar to images observed in typical gas-phase electron diffraction (GED). These spectra can be used to retrieve the positions of atoms in a molecule as in GED. Since infrared laser pulses of durations of a few femtoseconds are already available today, the study of these high-energy photoelectrons offers the opportunity of imaging the structure of transient molecules with temporal resolution of a few femtoseconds.

Quantitative rescattering theory for laser-induced high-energy plateau photoelectron spectra

A comprehensive quantitative rescattering (QRS) theory for describing the production of high-energy photoelectrons generated by intense laser pulses is presented. According to the QRS, the momentum distributions of these electrons can be expressed as the product of a returning electron wave packet with the elastic differential cross sections (DCS) between free electrons with the target ion. We show that the returning electron wave packets are determined mostly by the lasers only and can be obtained from the strong field approximation. The validity of the QRS model is carefully examined by checking against accurate results from the solution of the time-dependent Schr\"odinger equation for atomic targets within the single active electron approximation. We further show that experimental photoelectron spectra for a wide range of laser intensity and wavelength can be explained by the QRS theory, and that the DCS between electrons and target ions can be extracted from experimental photoelectron spectra. By generalizing the QRS theory to molecular targets, we discuss how few-cycle infrared lasers offer a promising tool for dynamic chemical imaging with temporal resolution of a few femtoseconds.

Robust carrier-envelope phase retrieval of few-cycle laser pulses from high-energy photoelectron spectra in the above-threshold ionization of atoms

The two-dimensional momentum distributions of high-energy photoelectrons generated in the above-threshold ionization of atoms by intense laser pulses are analysed as resulting from the elastic backscattering of laser-induced returning electrons. Using this quantitative rescattering theory, we show that the returning electron wave packets are entirely determined by the properties of the laser pulses, including the absolute value of the carrier-envelope phase (CEP). We then present a robust method to precisely retrieve the absolute phase of few-cycle pulses by analysing separately the CEP dependence of the electron spectra emitted on the left and on the right directions along the laser polarization axis. In addition, our approach offers the possibility of measuring the laser peak intensity and pulse duration with an estimated error of a few per cent.

Dehydrogenation of Cyclohexene on Platinum Nanoclusters on a Thin Film of Al2O3/NiAl(100)

Using a scanning-tunneling microscope, reflection high-energy electron diffraction and photoelectron spectra with synchrotron radiation, we investigated the temperature dependence of the dehydrogenation of cyclohexene (C6H10) adsorbed on Pt nanoclusters supported on an ultra-thin film of Al2O3/NiAl(100). The Pt clusters, grown by vapor deposition, are structurally ordered and exhibit a mean diameter 2.2 nm and height 0.4 nm. The progress of dehydrogenation was monitored through the temporal variation of C 1s photoelectron spectra; analysis of these features revealed that the dehydrogenation of cyclohexene with increasing sample temperature occurs as a sequential process beginning around 150 K, a temperature significantly less than that for Pt single-crystal surfaces. The dehydrogenation behavior, particularly the decomposition into elemental carbon, is found to vary with Pt coverage.

Bulk sensitive photo emission spectroscopy of [formula omitted] compounds

This work reports about bulk-sensitive, high energy photoelectron spectroscopy from the valence band of CoTiSb excited by photons from 1.2 to 5 keV energy. The high energy photoelectron spectra were taken at the KMC-1 high energy beamline of BESSY II employing the recently developed Phoibos 225 HV analyser. The measurements show a good agreement to calculations of the electronic structure using the LDA scheme. It is shown that the high energy spectra reveal the bulk electronic structure better compared to low energy XPS spectra.

Multielectron excitations in high-energy photoelectron spectra of CO adsorbed on Ni(100).

High-resolution x-ray-excited core-level shake-up and valence-electron spectra of CO adsorbed on Ni(100) in the c(2\ifmmode\times\else\texttimes\fi{}2) structure are presented. A number of newly resolved structures are reported. The C 1s and O 1s shake-up spectra show pronounced differences. The shake-up transitions are treated as local molecular excitations in the presence of the core hole. It is proposed that transitions from the 2${\ensuremath{\pi}}^{\mathrm{*}}$ screening orbital into 3p and other higher states with Rydberg character give rise to the most intense shake-up peaks in adsorbed CO. In the C 1s spectrum a low-energy satellite is identified as an excitation from bonding to antibonding 2${\ensuremath{\pi}}^{\mathrm{*}}$-3d combinations. The high-energy shake-off continua reveal several broad structures which are interpreted as autoionizing or shape resonances in the shake-off continua. These features are compared with thresholds observed in photon-stimulated-ion-desorption spectra for adsorbed CO. The difference spectrum between the valence region of Ni with and without adsorbed CO reveals several features over an energy range of 40 eV. The 3\ensuremath{\sigma} state and the correlation satellites are compared with features in the autoionizing spectra at the core-level thresholds.

High-energy photoelectron spectroscopy of some antimony compounds

High-energy photoelectron (p.e.) spectra have been obtained for a number of compounds of antimony. The antimony 3d(,5//2) binding energies range from 542.9, 533.3 eV for [Et4N][SbF6] to 538.6, 529.0 eV for Bun3Sb, but there is little correlation with the formal oxidation state. Assignment of the oxidation state of antimony on the basis of X-ray p.e. data alone is not possible with certainty and even gross structural differences may remain undetected by this method.

On the calculation of the satellite peaks observed in the high energy photoelectron spectra of small molecules

The shake-up peaks which are observed to high binding energy of the main photoionization peak in the high energy photoeletron spectra of CO (carbon and oxygen core holes), H 2O and NH 3 have been interpreted by an extension of the singly excited configuration interaction method used previously in the study of the low-lying excited states of these molecules. The results obtained provide a good interpretation of the experimental spectra of these molecules in terms of many shake-up states. It is concluded that relaxed orbitals and an extensive basis set, including diffuse functions, should be used in the calculations in order to obtain good results.

Satellite peaks in the high energy photoelectron spectra of some small first row molecules

The gas phase high energy photoelectron spectra of CH4, NH3, H2O, N2, O2, CO and CO2 have been recorded, and in all cases weak satellite peaks to high binding energy of the main ionization peak are observed. These peaks are assigned to transitions to ionic states in which valence electron excitation as well as core ionization has occurred. The intensity and position of these peaks, relative to the main ionization peak have been estimated from ab initio UHF calculations on the core hole states, which in general allow assignment of the satellite peaks in terms of orbital transitions of the core hole ion.

The theoretical description of ionic states observed by high energy photoelectron spectroscopy

Core ionization potentials of some simple first-row molecules are calculated from ab initio molecular wavefunctions in a number of approximations. Valence orbital relaxation is included by performing configuration interaction calculations utilizing the virtual orbitals of the neutral species. By this method, with the use of an atomic orbital basis of double zeta quality or better, very good agreement with experimental core binding energies is obtained. The origin of the satellite peaks observed in high-energy photoelectron spectra is discussed with the aid of these calculations.

Theoretical study of the geometry of PH3, PF3 and their ground ionic states

The geometries of PH3, PF3 and their ground ionic states have been calculated using ab initio SCFMO wavefunctions. All four species are found to be pyramidal, the calculated barriers to inversion being sensitive to the inclusion of d functions in the basis. The calculated potential energy diagrams are found to offer a satisfactory interpretation of the high resolution low energy photoelectron spectra of these molecules.

Satellite phenomena in the high energy photoelectron spectra of tetramethyl-p-phenylenediamine (TMPD), tetracyanoquinodimethane (TCNQ), and their derivatives. Experimental and theoretical study

The high energy photoelectron spectra of tetramethyl-p-phenylenediamine (TMPD) and its singly and doubly ionized derivatives are presented. The singly charged species (Wurster's Blue) exhibits a pronounced satellite on the high binding energy side of the N1s peak. This satellite, together with the satellites reported previously in the N1s spectra of tetracyanoquinodimethane (TCNQ) and its radical anion salts are attributed to “shake-up” in which an electron in the highest filled molecular orbital is promoted to the first virtual orbital, accompanying core ionization. The assignments are based on modified sudden approximation calculations. The nature of the electronic interactions in these compounds is discussed in the light of the ESCA experiments.

Interpretation of high energy photoelectron spectra satellite peaks by semi-empirical molecular orbital calculations

The sudden approximation is used to calculate the position and intensity of satellites accompanying core ionization in a series of molecules utilizing wavefunctions calculated in the INDO approximation. The results show semi-quantitative agreement with experiment and allow the assignment of various satellites to particular excitations accompanying primary ionization (shake-up). It is shown that in the case of degenerate hole states a localized hole state approximation is needed in order to interpret the satellites.

X-Ray induced photoelectron spectra of tetracyanoquinodimethane (TCNQ) and its complexes

Detailed studies of core-electron profiles in the high-energy photoelectron spectra of TCNQ and eighteen of its complexes have been carried out. In all these solids, satellites appear 2 to 4 eV on the higher-binding energy side of both the N1s and C1s main peaks. The satellites are attributable to a shake-up process involving intramolecular transitions between the π-electron valence molecular orbitals in both neutral and ionic TCNQ species. Except in a few cases, which are discussed, intermolecular (charge-transfer) interaction plays a minor role in the core-level, photoelectron spectra of the complexes.Valence band measurements of some of the complexes, the temperature-dependence of some N1s profiles as well as the splitting of some of the metal ion core-levels, are also briefly discussed.

The high energy photoelectron spectra of molybdenum in some [formula omitted] systems

The high energy photoelectron spectra of molybdenum in some [formula omitted] systems