Photoelectron recapture as a tool for the spectroscopy of ionic Rydberg states (original) (raw)
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Study of second-step Auger transitions in Auger cascades following 1s → 3p photoexcitation in Ne
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
We present the results of high-resolution measurements of the low-energy part of the Auger electron spectrum generated by photoexcitation of the 1s −1 3p resonance in Ne. The spectrum was measured in the energy range of 10-33 eV where mainly the electrons from the second-step Auger transitions of the cascades 1s −1 3p → 2s2p 5 np → 2s 2 2p 4 and 1s −1 3p → 2s 0 2p 6 np → 2s2p 5 (n = 3, 4) are detected. High resolution allows us to study the multiplet structure of the transitions and to determine the widths of the intermediate states of the Ne + ion. Anisotropy of the angular distribution of Auger electrons is determined for all of the lines observed. The results are in reasonably good agreement with MCDF calculations.
Physical Review A, 2006
New high-resolution experimental results on Ne 1s near-threshold photoionization with subsequent decay into a 2p 4 ( 1 D2)n ′ p or 2p 4 ( 1 D2)ε ′ p state are presented. The population of Rydberg states up to n ′ = 12 is determined as a function of excess energy. These data allow one to track in detail the transition from resonant Auger decay going along with shake-up of the spectator electron to shakedown and photoionization with recapture of the photoelectron. Results are in good agreement with a time-dependent quantum mechanical theory of Auger decay in the presence of a slow photoelectron.
Multiplet exchange Auger transitions following resonant Auger decays in Ne 1s photoexcitation
Secondary electron emission with very low kinetic energy (KE) has been measured in the Ne 1s photoexcitation region. A new decay channel for Auger transitions following Ne 1s to 3p excitation has been identified using a two-dimensional mapping technique, in which slow Auger electron signals are displayed as functions of electron kinetic energy and photon energy. Electrons with about 0.68 eV KEs have been ascribed to multiplet exchange Auger electrons from the 2p −2 (1 S)3d state. This state is formed through the resonant Auger transition from the 1s −1 3p state, in which the excited 3p electron changes its azimuthal quantum number. Another cascade Auger decay of multiplet exchanging was found as electron emission of about 2.0 eV KEs; 2p −2 (1 S)4p → 2p −2 (3 P) + e −. Several cascade decays were found to occur via the photoexcitation into 1s −1 4p and 1s −1 5p states.
The Astrophysical Journal, 2017
Single, double, and triple photoionization of Ne + ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon-ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K-and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne + (s s p 1 2 2 S 2 6 2 1 2) level, for example, requires cooperative interaction of at least four electrons.
Photoabsorption and resonant photoemission in the region of Ne 1s double excitations
Journal of Electron Spectroscopy and Related Phenomena, 2005
The absolute photoabsorption cross-sections of Ne in the regions 865-873 (1s Rydberg states) and 900-940 eV (double excitations) have been measured. Several new double excitation states were detected, including a very weak member of the series converging to the 1s2p 5 3s conjugate shake-up ion state. States were also observed above the 1s2p 5 double ionisation potentials, and are assigned to the 1s2snsn p series. At the first 1s2p 5 3p 2 double excitation state, the partial ionisation cross-section for the 1s −1 ion state resonates. The behaviour of the cross-section and Fano profile are analysed by a theoretical calculation using the time-independent scattering formalism.
Photoionization of Ne^{+} using synchrotron radiation
Physical Review A, 2002
Absolute measurements of cross sections for photoionization of a statistical admixture of Ne ϩ in the 2 P 3/2 o ground state and the 2 P 1/2 o metastable state are reported in the energy range 40-71 eV at photon energy resolutions ranging from 22 meV to 2 meV. The experiments were performed using synchrotron radiation from an undulator beamline of the Advanced Light Source with a newly developed ion-photon-beam endstation. The data are characterized by multiple Rydberg series of autoionizing resonances superimposed upon a direct photoionization background cross section where some of the observed resonance line shapes show evidence of interference between the direct and indirect photoionization channels. The resonance features are assigned spectroscopically, and their energies and quantum defects are tabulated. The experimental photoionization cross sections are in satisfactory agreement with the predictions from theoretical calculations performed in intermediate coupling using the semirelativistic Breit-Pauli approximation with ten states. The resonances nearest to the ionization thresholds exhibit anomalous behavior with respect to their positions and strengths due to the presence of interloping resonances associated with higher-lying ionic states causing disruption of the regular Rydberg spectral pattern.
Physical Review A, 2003
Angle-resolved resonant Auger-electron spectroscopy has been carried out on the nitrogen molecule at selected photon energies around 419 eV, where a 1s core electron and two valence electrons are promoted into the lowest unoccupied molecular orbital 1 g. Significant enhancement of a specific band, which cannot be disentangled in direct photoionization, is observed at a binding energy of 37.6 eV, with a value of the anisotropy parameter  much smaller than 2. We assign this new band to the transition to a doubly excited cationic state of N 2 , in which two of the excited valence electrons remain in the 1 g orbital, proposing a ''double spectator'' type decay mechanism. This observation shows how to preferentially probe multiply excited configurations of cations using multiple resonant excitation.
Photoexcitation study of the 4s 2 S 1/2 state of atomic sodium
Journal of Physics B: Atomic, Molecular and Optical Physics, 2008
We report the first measurements of oscillator strengths for 4s 2 S 1/2 → np 2 P 1/2,3/2 (19 n 57) Rydberg transitions in atomic sodium using a thermionic diode ion detector in conjunction with an Nd:YAG pumped dye laser system. The f-values have been calibrated with the measured photoionization cross-section from the 4s 2 S 1/2 excited state at the first ionization threshold as 0.65(0.10) Mb. The binding energy of the 4s 2 S 1/2 level is determined as 15 709.444(8) cm −1 by employing the Rydberg relation to the observed np 2 P 1/2,3/2 Rydberg series. Addition of the binding energy to the known energy of the 4s 2 S 1/2 level yields the first ionization potential of sodium as 41 449.44(1) cm −1 , which is in excellent agreement with the recognized value.