Effects of double pulses in strong-field photoionization

The dynamics of the bound state population and the photoelectron energy spectra due to photoionization by a double pulse are calculated for a model atomic system. The splitting of the ATI peaks due to the structure of the pulse is presented and discussed.     

Double photoionization into double core-hole states in Xe

Double photoionization (DPI) leading to double core-hole states of Xe2+ 4d(-2) has been studied using a magnetic bottle time-of-flight spectrometer. The assignments of the Xe2+ 4d(-2) states are confirmed by the Auger lines extracted from fourfold coincidences including two photoelectrons and two Auger electrons. It is estimated that the core-core DPI into Xe2+ 4d(-2) at a photon energy of 301.6 eV has a favored cross section of about 0.3 MB. The intense core-core DPI is due to mixing of the 4d(-2) continuum with the 4p single photoionization, which is manifested in the relative intensities of the Xe2+ 4d(-2) components.     

Calculation of resonant structure of a double photoionization

Using many-body perturbation theory, we give the first calculation for the resonance structure into the double photoionization continuum in the 2s → 3p resonance region in neutral sodium. This resonance structure results from the interference between the one step direct double photoionization continuum and the resonant Auger process. The coupled equation method has been improved to calculate this interference by the summation of specific classes of diagrams of perturbation theory to infinite order. We find that the dominant contribution to resonance comes from a super-Coster-Kronig decay. Theoretical results are in good agreement with experiment.     

Back-to-back emission of the electrons in double photoionization of helium

We calculate the double differential distributions and distributions in recoil momenta for the high energy non-relativistic double photoionization of helium atom. We show that the results of recent experiments provide the pioneering experimental manifestation of the quasifree mechanism for the double photoionization which was predicted long ago in our papers. This mechanism provides a surplus in distribution over the recoil momenta at small values of the latter, corresponding to nearly ??back-to-back?? emission of the photoelectrons. Also, in agreement with previous analysis we demonstrate that this surplus is due to the quadrupole terms of the photon-electron interaction. We present the characteristic angular distribution for the back-to-back electron emission. The confirmation of the quasifree mechanism existence opens a new area for exciting experiments, which are expected to increase our understanding of the electron dynamics and of the bound states structure.     

Pd-Na/F double exploding foil photoionization experiment

By means of two exploding foils, we have achieved inner-shell photoionization of Zn-like Pd resulting in the soft X-ray transition 3d ⁹4s ² 3d ¹⁰4p at 46 Å.     

Synchrotron radiation VUV double photoionization of some small molecules

The VUV double photoionizations of small molecules (NO,CO,CO2 ,CS2 ,OSC and NH3 ) were investigated with photoionization mass spectroscopy using synchrotron radiation. The double ionization energies of molecules were determined with photoionization efficiency spectroscopy. The total energies of these molecules and their parent dications (NO2+ ,CO2+ ,CO2+2 ,CS2+2 ,OSC2+ and NH2+3 ) were calculated using the Gaussian 03 program and Gaussian 2 calculations. Then,the adiabatic double ionization energies of the molecules were predicated by using high accuracy energy mode. The experimental double ionization energies of these small molecules were all in reasonable agreement with their respective calculated adiabatic double ionization energies. The mechanisms of double photoionization of these molecules were discussed based on a comparison of our experimental results with those predicted theoretically. The equilibrium geometries and harmonic vibrational frequencies of molecules and their parent dications were calculated by using the MP2 (full) method. The differences in configurations between these molecules and their parent dications were also discussed on the basis of theoretical calculations.     

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.     

Experimental observation of post-collision interaction and interference effects in resonant double photoionization processes

The combined effects of post-collision interaction in the final state and interference due to the indistinguishability of the two electrons have been studied in a selected case of resonant double photoionization of neon. In our coincidence experiments, the photo- and Auger-electron pair was measured when the two electrons have nearly equal energy and are ejected at small mutual angle. The obtained energy distributions exhibit a strong interplay of post-collision interaction and interference effects, in agreement with the theoretical prediction of Sheinerman and Schmidt [J. Phys. B 30, 1677 (1997)] made on beryllium.     

Electron angular distributions in double photoionization: Use of effective Sommerfeld parameters

We present calculations of the fivefold differential cross-section (FDCS) for double photoionization of helium at excess energies of 6 and 20 eV above threshold. Our results are obtained using for the final double-continuum state a product of three Coulomb wave functions, with the Sommerfeld parameters modified to describe the strength of interaction of any two particles affected by the third particle. Our calculations are compared with recent absolute measurements by D?rner et al. (Phys. Rev. A 57, 1074 (1998)), both in coplanar and non-coplanar geometries. Very good agreement is obtained for the shape of the angular distributions, and differences in the absolute magnitude exist in comparison with the standard choice of Sommerfeld parameters. Received: 17 July 1998 / Received in final form and Accepted: 23 October 1998     

Large molecules reveal a linear length scaling for double photoionization

We have measured the ratio of doubly to singly charged parent ions of benzene, naphthalene, anthracene, and pentacene using monochromatized synchrotron radiation up to 30 eV above the corresponding threshold. Our measurements show a striking similarity between the ratio of doubly charged to all parent ions and the ratio for helium. Moreover, the magnitudes of the ratios for these molecules scale linearly with their lengths with an amazing accuracy. A high ratio, i.e., a high relative double-photoionization probability, makes a molecule an important source of low-energy electrons that can promote radiation damage of biomolecules [B. Bouda?ffa et al., Science 287, 1658 (2000)].