F. Vollweiler

Neutral photodissociation of O2 Rydberg states accompanied by changes of the Rydberg electron's quantum numbers n and l

Abstract The neutral dissociation (ND) behavior of the Rydberg states converging to the c 4 Σ − u state in O2+ was investigated using photon-induced fluorescence spectroscopy (PIFS). It was found that the dissociation of Rydberg states n dσ g 3 Σ u − with v=1 and n sσ g 3 Σ u − with v=0/1 leads, in the observed fluorescence wavelength region from 90 to 105 nm, mainly to an excited OI fragment either in the ( 4 S o ) (n+1)/n s 3 S o state or ( 4 S o ) n/(n−1) d 3 D o state for the ndσg and nsσg molecular Rydberg states, respectively. The observed change of n corresponds to the conservation of the effective quantum number n ∗ .

Lifetimes of the ns1 np6 2S1/2 states of singly ionized argon, krypton and xenon

The lifetimes of the ns1 np6 2S1/2 states of Ar II, Kr II and Xe II were determined by measuring the fluorescence decay curves after selective excitation with pulsed monochromatized synchrotron radiation. The lifetimes are Ar = (4.684±0.019) ns, Kr = (30.78±0.17) ns, and Xe = (35.93±0.20) ns. Calculations performed within the configuration interaction approach show the strong dependence of the calculated lifetimes on the configuration interaction. It is proposed to use the precise lifetime values for a test of future calculations of the effective value of the Coulomb interaction of electrons.

Angular distribution of the fluorescence radiation of Kr II satellite states

Photon-induced fluorescence spectroscopy was applied for the first time to investigate the anisotropy of VUV radiation emitted from Kr II satellite states with total angular momentum after the photoionization of the Kr atom by linearly polarized synchrotron radiation near the 4s threshold. The measurements showed that the sign of the alignment parameter is practically independent of the exciting-photon energy for the ionic state with , whereas for the states with the alignment parameter changes sign with varying energy. Simple formulae connecting the angular distribution parameter and the alignment parameter with the kinematics of our experiment and with quantities describing the dynamics of the photoionization were derived in closed form. Partial and total cross sections for the photoionization of 4p, 4s and several satellite levels were calculated taking into account many-electron correlations and doubly-excited states. For the satellite states with the dependence of the angular distribution parameter on the exciting-photon energy was calculated. Good overall agreement between theory and experiment was obtained.

Alignment of ions after autoionization decay of atomic resonances: II. The 3d95/25p (J = 1) resonance in Kr

The alignment of the 5p4 6p levels after the decay of the Xe I 4d9 5/2 6p(J = 1) resonance was investigated experimentally and theoretically. The angular distribution of the visible fluorescence radiation was used to measure the alignment. To calculate the measured quantities the multi-step model was applied, taking account of the relativistic effects within the Pauli-Fock approximation. The influence of the cascade effects on the population of the 5p4 6p levels was estimated.

Photoionization of Ar and Ar-like ions near the 3s-threshold

The absolute cross sections for the 3s-photoionization and the 3p-photoionization of the Ar atom and the Ar-like ions K+ and Ca2+ are calculated. The calculation is performed within the configuration-interaction technique using the Pauli-Fock atomic orbitals. The simultaneous analysis of the calculated and measured total and partial cross sections yields the interpretation of the prominent resonances observed in a recent experiment on Ar above the 3s-threshold.

Fine-structure selectivity of neutral dissociation with excitation observed in O2

The absorption cross section of O2 and the O I (4So)3s 3So1→2p4 3PJ emission cross section were investigated near the threshold for neutral dissociation into the O I (4So)3s 3So1 state with a very narrow bandwidth (0.9 meV) of the exciting radiation. It was possible for the first time to resolve the fine-structure (FS) components of vibrational levels in the emission cross section and, in addition, to determine their relative intensities. A certain degree of selectivity in the population of FS components was observed. Furthermore, an absolute cross section for the dissociation into the fragments in the O I ground state or the metastable O I (4So)3s 5So2 state was estimated.

Improved resolution of the prominent Ar 3s-electron threshold energy range photoionization resonances

Abstract The Ar 3s-electron photoionization cross section was measured in the photon energy range from threshold to 35 eV applying photon induced fluorescence spectroscopy. The bandwidth of the exciting photons was 15 meV, allowing a strong resonance enhancement of the cross section close to threshold. The energetic positions of the resonances were determined by a profile analysis.

Threshold scan of the Ne 2s-electron photoionization cross section

Abstract The photoionization of the Ne 2s-electrons was studied from threshold to 1 eV above threshold. The technique of photon-induced fluorescence spectroscopy was applied. Pronounced structures were observed resulting from autoionization of doubly excited atomic states. A threshold cross section of 0.17 Mb was determined.

High-resolution study of the prominent near-threshold resonances in the Ar 3s-electron photoionization

Abstract The absolute Ar 3s-electron photoionization cross section was measured in the exciting-photon energy range from 30.65 to 31.75 eV by photon-induced fluorescence spectroscopy (PIFS). The bandwidth of the exciting synchrotron radiation was 4.8 meV. The profiles of the resonances observed in the Ar 3s-electron photoionization were compared with the profiles of the resonances in the total photoabsorption.

Perturbation theory study of triple photoionization: I. Two-step approximations in triple photoionization of Kr in the exciting-photon energy region of Kr I resonances (90 - 100 eV)

The two-step triple photoionization (TPI) process is investigated in the framework of many-body perturbation theory for the first time. Results on TPI partial cross sections from the Kr ground state to the fluorescing states of the Kr IV configuration are obtained by numerical calculations in the energy range of Kr I resonances. Several mechanisms of two-step TPI are discussed, of which the low-energy double-Auger transitions are investigated in detail. The energy distribution functions of the Auger electrons for the different orbital momenta of the ejected two Auger electrons as well as the total transition probability are presented. Comparison of the calculated TPI cross section with experimental data obtained by photon-induced fluorescence spectroscopy demonstrates quite clearly the shortcomings of the two-step approximation for a quantitative description of the process, at least in the energy region under consideration. Nevertheless qualitative agreement has been achieved which explains in principle the new fluorescence transitions in Kr IV observed after excitation of the atom by photons of an energy from 90 to 100 eV.