W. Kielich

Large impact of the weak direct photoionization on the angularly resolved CO+(A 2Π) de-excitation spectra of the CO*(1σ−12π) resonance

Interference between the direct and resonant amplitudes for the population of the CO+(A 2Π) state in the vicinity of the O 1s → 2π excitation of CO* is studied by an ab initio theoretical approach. The weak direct photoionization induces Fano–Shore-type profiles resulting in long-range exciting-photon energy dependences of the computed angular distribution parameters for the CO+(A 2Π) photoelectrons, βeA(ω), and for the subsequent CO+(A 2Π → X 2Σ+) fluorescence, β2XA(ω). In the presence of direct photoionization, the lifetime vibrational interference causes substantial variations of the computed parameter βeA(ω) across the positions of the CO*(vr) vibronic states. Theoretical results are in qualitative agreement with the vibrationally and angularly resolved CO+(A 2Π) resonant Auger electron spectra recorded in the Raman regime at different exciting-photon energies across the CO* resonance.

Strong interference effects in the angularly resolved Auger decay and fluorescence emission spectra of the core-excited NO molecule

Angular distributions of Auger electrons and subsequent fluorescence photons are studied theoretically and experimentally in the vicinity of the core excitations of NO. In the calculations, lifetime vibrational interference and electronic state interference were taken into account ab initio. The interference between excitation and deexcitation amplitudes for transitions via symmetry-different intermediate resonances 1s?12?2(2?, 2??), which is forbidden in the solid-angle-averaged or magic-angle-recorded decay spectra, plays a crucial role in the formation of the angularly resolved decay spectra. Experimentally, angular distribution parameters for the NO+(A1? ? X1?+) fluorescence induced by linearly polarized synchrotron radiation are determined in the vicinity of the N*O resonance in the Raman regime for core excitation. Theoretical results are in good agreement with the present experimental fluorescence spectra and with the available vibrationally and angularly resolved resonant Auger electron spectra.

Predominant dissociation of the CO*(D2Π)n(d/s)σ Rydberg states into atomic excited Rydberg fragments with the same effective principal quantum number

Dissociation of the CO molecule excited in the photon energy range between 20 eV and 25 eV is investigated by photon-induced fluorescence spectroscopy (PIFS) detecting dispersed fluorescence from C I* 2s22p1n(d/s) fragments in the spectral range of 115–135 nm. First experimental indications were found for a predominant dissociation of the CO*(D2Π)n(d/s)σ Rydberg states into the Rydberg states of the neutral C I atom conserving the effective principal quantum number n* = n − δ of the Rydberg electron. Such a process has as yet been verified only for the dissociating molecular Rydberg series (c4Σ−u)n(d/s)σg3Σ−u in O*2 (H Liebel et al 2000 Phys. Lett. 267 267). The selective dissociation of the molecular Rydberg states into atomic ones is interpreted by theoretical potential energy curves of the CO+ ion and molecular orbitals of Rydberg electrons computed within the single-centre approach.

Fluorescence cascades after excitation of XeII 5p46p satellite states by synchrotron radiation

Dispersed fluorescence excitation functions and the relative total ion yield as a function of the exciting-photon energy in the range between 26.150 eV and 26.400 eV have been measured for Xe after excitation with monochromatized synchrotron radiation with the very narrow bandwidth of 2.5 meV. Fluorescence excitation functions have been simultaneously measured in the VUV and in the visible spectral range to track and identify radiative decay cascades after photoionization into excited XeII states of 5p46p electron configuration. Additionally the angular fluorescence distribution parameter βfl-parameter was experimentally determined for some of the observed fluorescence lines.

Symmetry-Forbidden Electronic State Interference Observed in Angularly Resolved NO{sup +}(A {sup 1{Pi}}) Deexcitation Spectra of the N*O(2{sigma}{sup -1}2{pi}{sup 2}) Resonance

Quantum mechanical interference between different pathways in inner-shell resonance excitation-deexcitation spectra is a realization of a double-slit experiment on the atomic scale. If the intermediate inner-shell resonances are of different symmetries, this interference is symmetry forbidden in the solid-angle-averaged or magic-angle-recorded deexcitation spectra. It has, however, been suggested that interference may by observable in off-magic-angle-recorded spectra. Here, we prove this interference in angularly resolved deexcitation spectra of the 2σ(-1)2π(2)(2Δ,2Σ±) resonances of N*O by a quantitative comparison between ab initio calculations and experiment.

Observation and identification of odd XeI Rydberg resonances near 5s-threshold

Photoionization cross sections for the production of main 5s line and some 5p4 5d/6s satellites of XeII in the region of the 5s-photoionization threshold have been measured by photon-induced fluorescence spectroscopy (PIFS) with extremely high primary resolution. The most pronounced features in the experimental spectra were interpreted on the basis of theoretical calculations.