H. Liebel

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.

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.

VUV-fluorescence spectroscopy of O2 photodissociation into neutral excited fragments between 17 and 19 eV

Photodissociation processes of O2 at exciting-photon energies between 17 and 19 eV were investigated through dispersed fluorescence excitation spectra in the VUV spectral range, by measuring the intensities of fluorescence lines emitted by neutral excited dissociation fragments between 90 and 105 nm as a function of the exciting-photon energy. The dissociation processes were found to be strongly influenced by predissociation of molecular Rydberg states converging to the O2+ b 4Σg− state, whereas direct dissociation processes resulting from repulsive potentials in the Franck–Condon region were found to be weak. The measured fluorescence excitation functions as a measure for O2 photodissociation were compared with photoionization and ion pair formation cross sections and it was found that the fluorescence excitation functions show similarities to the ion pair formation cross sections.

Double photoionization of N2 into the N22+ D 1Σu+-state

Double photoionization of N2 into the N22+D1Σ u+-state as a function of the exciting-photon energy has been investigated experimentally and theoretically. Photon-induced fluorescence spectroscopy using monochromatized synchrotron radiation in the exciting-photon energy range between 50 and 66.5 eV and recording of the intensity of the dispersed VUV fluorescence between 145 and 167 nm has been carried out. Relative cross sections as a function of the exciting-photon energy have been determined. The experimental results are compared with ab initio calculations.

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.

Manifestation of doubly excited atomic states in the photoionization cross-sections of Ar, Kr and Xe in the vicinity of the subvalence ns-shell threshold

Abstract Energy dependences of the total and partial ns-photoionization cross-sections in the vicinity of the ns-subvalence shell threshold were measured for the rare-gas atoms using photon-induced fluorescence spectroscopy. A resolution of 4.5, 3, and 1 meV was attained for Ar, Kr and Xe, respectively. The experimental cross-sections exhibit many well-resolved resonances of different shapes which are connected with the photoionization through the doubly excited atomic states. Calculated photoionization cross-sections of Ar and Kr show that some resonances are determined by doubly excited states including strongly delocalized n′f-excited electrons.

Collisional quenching of the H(n = 3) atoms by molecular hydrogen: cross section measurements

The H(3l) + H2 collision has been investigated in the velocity range of 2-7 km s-1, at room temperature, through time-dependent fluorescence intensity measurements after pulsed excitation, at different pressures; the l-mixing cross sections and the cross sections for non-radiative quenching processes have been 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.