## Quasi-degenerate scaled opposite spin second order perturbation corrections to single excitation configuration interaction |

D. Casanova, Y. M. Rhee and M. Head-GordonJ. Chem. Phys. , (accepted for publication 2008) |

## Decoding sequential versus nonsequential two-photon double ionization of helium using nuclear recoil |

D. A. Horner, T. N. Rescigno, and C. W. McCurdy

*Phys. Rev. A* ** 77**, 030703 (2008)

Above54.4 eV, two-photon double ionization of helium is dominated by asequential absorption process, producing characteristic behavior in the single andtriple differential cross sections. We show that the signature ofthis process is visible in the nuclear recoil cross section,integrated over all energy sharings of the ejected electrons, evenbelow the threshold for the sequential process. Since nuclear recoilmomentum imaging does not require coincident photoelectron measurement, the predictedimages present a viable target for future experiments with newshort-pulse vacuum ultraviolet (vuv) and soft x-ray sources.

## Decoding sequential versus nonsequential two-photon double ionization of helium using nuclear recoil |

D. A. Horner, T. N. Rescigno, and C. W. McCurdy

*Phys. Rev. A* ** 77**, 030703(R)(2008)

Above54.4 eV, two-photon double ionization of helium is dominated by asequential absorption process, producing characteristic behavior in the single andtriple differential cross sections. We show that the signature ofthis process is visible in the nuclear recoil cross section,integrated over all energy sharings of the ejected electrons, evenbelow the threshold for the sequential process. Since nuclear recoilmomentum imaging does not require coincident photoelectron measurement, the predictedimages present a viable target for future experiments with newshort-pulse vacuum ultraviolet (vuv) and soft x-ray sources.

## Cross sections for short-pulse single and double ionization of helium

Wednesday, 19 March 2008

Philip L. Bartlett, Andris T. Stelbovics, T. N. Rescigno, and C. W. McCurdy

*Phys. Rev. A* ** 77**, 032710 (2008) Theapplication of an exterior complex scaling method to an atomicscattering problem with distinct rearrangement channels is reported. Calculations areperformed for positron-hydrogen collisions in an *s*-wave model employing anelectron-positron potential of *V*_{12}=−[8+(*r*_{1}−*r*_{2})^{2}]^{−1/2}, using the time-independent propagating exterior complexscaling method. This potential has the correct long-range Coulomb tailof the full problem and the results demonstrate that exterior-complex-scaling–basedmethods can accurately calculate scattering, ionization,and positronium formation cross sectionsin this three-body rearrangement collision.

## Cross sections for short-pulse single and double ionization of helium

Wednesday, 19 March 2008

Philip L. Bartlett, Andris T. Stelbovics, T. N. Rescigno, and C. W. McCurdy

*Phys. Rev. A* ** 77**, 032710 (2008) Theapplication of an exterior complex scaling method to an atomicscattering problem with distinct rearrangement channels is reported. Calculations areperformed for positron-hydrogen collisions in an *s*-wave model employing anelectron-positron potential of *V*_{12}=−[8+(*r*_{1}−*r*_{2})^{2}]^{−1/2}, using the time-independent propagating exterior complexscaling method. This potential has the correct long-range Coulomb tailof the full problem and the results demonstrate that exterior-complex-scaling–basedmethods can accurately calculate scattering, ionization,and positronium formation cross sectionsin this three-body rearrangement collision.

## Probing the nonlocal approximation to resonant collisions of electrons with diatomic molecules

Wednesday, 16 January 2008

Karel Houfek, T. N. Rescigno, and C. W. McCurdy

*Phys. Rev. A* ** 77**, 012710 (2008) Anumerically solvable two-dimensional model introduced by the authors [Phys. Rev.A **73**, 032721 (2006)] is used to investigate the validityof the nonlocal approximation to the dynamics of resonant collisionsof electrons with diatomic molecules. The nonlocal approximation to thismodel is derived in detail, all underlying assumptions are specified,and explicit expressions for the resonant and nonresonant (background) *T*matrix for the studied processes are given. Different choices ofthe so-called discrete state, which fully determines the nonlocal approximation,are discussed, and it is shown that a physical choiceof this state can in general give poorer results thanother choices that minimize the nonadiabatic effects and/or the backgroundterms of the *T* matrix. Background contributions to the *T*matrix, which are usually not considered in the resonant theoryof electron-molecule collisions, can contribute significantly not only to elasticbut also to vibrational excitation cross sections. Dissociative attachment crosssections, however, are found to be properly described in thenonlocal model with any choice of discrete state that minimizesthe importance of nonadiabatic effects and goes to the properlimit at large internuclear separation.

## Extracting amplitudes for single and double ionization from a time-dependent wave packet

Wednesday, 24 October 2007

A. Palacios,, T. N. Rescigno, and C. W. McCurdy

*Phys. Rev. A* ** 76**, 043420 (2007) Amethod is described for extracting double ionization amplitudes from aquantum wave packet for an atom after a short radiationpulse, but while the electrons are still interacting. The procedureinvolves the use of exterior complex scaling to effectively propagatethe field-free solution to infinite times, and allows the useof existing integral formulas for double ionization amplitudes for twoelectron atoms and molecules.