O. Wilhelmi

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 ∗ .

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.

Observation of coherence effects in the polarization of Lyman-α fluorescence following photodissociation of H2

Abstract The degree of linear polarization of Lyman-α fluorescence following photodissociation of H 2 into H(ls) + H(2 l ) has been measured at different excitation energies. The polarization as a function of the excess energy of the photofragments was observed to oscillate between about 0.1 and 0.2, in qualitative agreement with ab initio predictions of Glass-Maujean and Beswick.

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.

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.

High-resolution threshold-energy photoionization study of the Ne 2s-electron

Abstract The first evaluation of a high resolution threshold energy scan of the Ne 2s-electron partial photoionization cross section is presented, obtained from photon induced fluorescence spectroscopy. Strong resonance enhancement is observed, which is related with absorption resonances registered simultaneously.

COLLISIONAL QUENCHING OF H(3L) ATOMS BY MOLECULAR HYDROGEN

The de-excitation cross sections of H atoms colliding with molecular hydrogen were determined in the velocity range of 2-. At a mean velocity of the de-excitation cross sections are , and . The velocity dependence of the de-excitation cross sections observed in the experiment agrees with the quadrupole-H dipole interaction and with the quantum character of the molecular rotation.

Photofragmentation analysis from fluorescence-radiation angular-asymmetry parameter measurements of fine-structure resolved transitions on resonances

The angular asymmetry parameter of the photon-induced fluorescence radiation of fine-structure resolved satellite lines was measured from threshold up to 38.4 eV. It is well known that the cross sections of these valence shell satellites are dominated by the decay of aligned doubly excited states leading to an extremely complicated energy dependence. In contrast, we observe that the parameter becomes less structured with increasing total angular momentum J of the photoion. The measurements can be interpreted by a partial-wave analysis of the photofragmentation products. For the population of the ion state only photoelectrons are emitted on all resonances. For the population of the and the ion states the emission of the parity-unfavoured photoelectrons dominates.