Simultaneous electronphoton excitation of helium in a CO2 laser field

International audienceThe R-matrix Floquet method is used to study electron-impact excitation of helium in the presence of a CO 2 laser field, for collision energies between 19 and 21.5 eV and laser intensities of 10 7 and 10 8 W cm −2. Collision geometries with the electron incident at various angles to the laser polarization axis are considered. The signal for production of metastable states is in good agreement with the results of a low-frequency approximation and a semi-classical approach, while agreement with experiment is reasonable

R-matrix Floquet theory for laser-assisted electron-atom scattering

A new version of the R-matrix Floquet theory for laser-assisted electron-atom scattering is presented. The theory is non-perturbative and applicable to a non-relativistic many-electron atom or ion in a homogeneous linearly polarized field. It is based on the use of channel functions built from field-dressed target states, which greatly simplifies the general formalism.Comment: 18 pages, LaTeX2e, submitted to J.Phys.

Shape resonances in electron-hydrogen scattering

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Absolute cross sections and asymmetry parameters for photodetachment of excited C−^-(2^2D)

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Photodetachment of C− in the ground state

Absolute total cross sections and asymmetry parameters for photodetachment of C−(4So) have been measured using animated-crossed-beam and velocity map imaging techniques, for photon energies from threshold up to 6eV. The cross sections are 15% to 25% larger than earlier experimental results above 2.2 eV. They are in very good agreement with those from a new R-matrix calculation using polarized pseudostates

Theoretical study of electron-impact excitation of H(1s) into the states using a two-dimensional R -matrix propagator

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Absolute cross sections and asymmetry parameters for photodetachment of excited C- (2Do)

International audienceNegative ions are of fundamental interest for the understanding of electron correlation and also play an important role in domains such as astrophysics and atmospheric physics. Until recently, the photodetachment of the ground state of the carbon anion C− (4 S) suffered from long-standing discrepancies between the results of different calculations as well as between theory and experiment. New theoretical and experimental results were reported in [1], which are in very good mutual agreement, as well as a new description of the resonant process occurring for photon energies around 6 eV. Following on from of our previous work, we report here the results obtained for photodetachment of the excited state (2 D) of C− , in particular over the photon energy range from 0.5 to 2.5 eV where the disagreement between existing calculations are particularly pronounced [2, 3].A new theoretical description of the photodetachment process is provided, based on an R-matrix approach employing a basis set including polarized pseudostates to reproduce the polarizability of the carbon 3 P ground state. For the first time, absolute experimental cross sections have been obtained over the whole range, by the use of a modified Animated Crossed Beam (ACB) technique allowing for the presence of multiple components in the beam, while proper differential cross sections in the same range have been measured using our Velocity Map Imaging (VMI) spectrometer.We have also determined a more precise value for the electron affinity (EA) of the excited state, which is slightly higher than the pioneering experimental value of [4] and thus in strong disagreement with theoretical predictions of [5] and [3].[1] R. Marion et al., Phys. Rev. A 103, 023115 (2021).[2] C. A. Ramsbottom et al., J. Phys. B: At. Mol. Opt. Phys. 26, 4399 (1993).[3] H.-L. Zhou et al., Phys. Rev. A 72, 032723 (2005).[4] D. Feldmann, Chem. Phys. Lett. 47, 338 (1971).[5] T. Carette and M.R. Godefroid, Phys. Rev. A 83, 062505 (2011)

Two-dimensional R -matrix propagator: Application to electron-hydrogen scattering

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Sequential double photodetachment of He− in elliptically polarized laser fields

Four-photon double detachment of the helium negative ion is investigated experimentally and theoretically for photon energies where the transient helium atom is in the 1s2s 3S or 1s2p 3Po states, which subsequently ionize by absorption of three photons. Ionization is enhanced by intermediate resonances, giving rise to series of peaks in the He+ spectrum, which we study in detail. The He+ yield is measured in the wavelength ranges from 530 to 560 nm and from 685 to 730 nm and for various polarizations of the laser light. Double detachment is treated theoretically as a sequential process, within the framework of R-matrix theory for the first step and effective Hamiltonian theory for the second step. Experimental conditions are accurately modeled, and the measured and simulated yields are in good qualitative and, in some cases, quantitative agreement. Resonances in the double detachment spectra can be attributed to well-defined Rydberg states of the transient atom. The double detachment yield exhibits a strong dependence on the laser polarization which can be related to the magnetic quantum number of the intermediate atomic state. We also investigate the possibility of nonsequential double detachment with a two-color experiment but observe no evidence for it

Electron-impact excitation of the ground state into the states of between the n = 2 and n = 4 thresholds

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