S. Mickat

De-excitation dynamics of Rydberg states in O2: II. Vibrational and rotational structure of 2σ−1u(c4Σ−u)(ns/nd)σg3Σ−u(v = 0, 1) states

The competition between autoionization and neutral dissociation (ND) of the vibronic Rydberg states 2σ−1u(c4Σ−u)(ns/nd)σg3Σ−u(v = 0, 1) has been investigated using an experiment of photon-induced fluorescence spectroscopy (PIFS) and the simultaneous measurement of the photo ion yield. The experiments were performed with monochromatized synchrotron radiation from BESSY II with a very narrow bandwidth of ΔE = 1.5 meV at 23 eV where it was possible to observe single rotational branches. The experiments are compared to ab initio calculations for the partial autoionization and dissociation widths and to the corresponding simulations of the spectroscopic shape of the rovibronic branches. For more precise calculations of the dissociation widths, diabatic potential curves of the 2σ−1u(c4Σ−u) states of the O+2 are extracted from the adiabatic ones and improved calculations for molecular orbitals of the Rydberg and Auger electrons are used.

The interference effects in the alignment and orientation of the Kr II 4p45p states following Kr I 3d9np resonance excitation

The energy dependence of the alignment parameter A20 for the Kr II 4p45p(E 1J1) states following excitation in the Raman regime with the exciting-photon energy passing through the Kr I 3d9np resonances was investigated theoretically and experimentally. Interference between the resonance and direct photoionization channels explains the dependence of A20 on the excitation energy. Experimentally, A20 was determined after the analysis of 5p–5s fluorescence decay of the 4p45p(E 1J1) states excited with monochromatized synchrotron radiation. The band pass of the synchrotron radiation was set to 10 meV which is smaller than the natural width of the 3d9np resonances (~83 meV). Additionally, a strong energy dependence was predicted for the orientation parameter O10 as well as for the angular distribution parameter of photoelectrons, βe, for several 4p45p(E 1J1) ionic states.

Partial wave analysis of the Kr I 3d5/295p 3/2 → Kr II 4p4(1D)5p 2F 7/2 decay, based on orientation and alignment transfer

The orientation parameter, O10, and the alignment parameter, A20, of the Kr II 4p4(1D)5p 2F7/2 state populated in the resonant Auger decay on the Kr I 3d5/295p 3/2 (J = 1) resonance were measured, using photon-induced fluorescence spectroscopy (PIFS) and a Stokes parameter analysis. These parameters allow a partial wave analysis yielding a dominating contribution of the g9/2 electron partial wave. An excellent agreement with calculated values is obtained. A special feature of the present experiment is the measurement and analysis of circularly polarized light in a PIFS study.

Observation and identification of doubly excited KrI 4s24p45snł Rydberg series

Dispersed Kr VUV-fluorescence excitation spectra and photoion yields were recorded in the exciting photon energy range between 28.4 eV and 28.7 eV with extremely narrow bandwidth (1.7 meV at 28.55 eV) of the monochromatized synchrotron radiation used as the exciting photon source. Two series of doubly excited KrI states were observed and identified as the 4s24p4 (3P) 5s 4P1/2 np and the 4s24p4(3P)5s 2P3/2 np series.

Partial wave analysis of interfering Kr 3d95p resonant Raman Auger transitions based on measurements of alignment and orientation parameters within the natural line width

The alignment parameter A20 and the orientation parameter O10 for the 4p4(1D)5p2F7/2 and the 4p4(1D)5p2D5/2 states of Kr+ populated in resonant Auger transitions from 3d95p/6p photo-excited states of Kr were measured at BESSY II for photon energies between 91 eV and 92.8 eV. The method of fluorescence polarimetry was applied. A bandwidth of the exciting photons of 10 meV allowed to study A20 and O10 within the natural line width. Interference effects for resonances overlapping due to lifetime broadening were predicted and observed even when separated by 15 times the natural line width. The relative contribution of the three allowed electron partial waves was derived from A20 and O10 as a function of the exciting-photon energy and compared with the calculated contributions. The resulting good overall agreement between experiment and prediction is considered as a noticeable improvement of the understanding of excitation and decay of the prominent Kr 3d95p resonances.

Interference between resonant Raman Auger decay and direct excitation manifested in orientation and alignment of KrII 4p4(1D)5p 2P3/2 ions

The orientation parameter O10 for the 4p4(1D)5p2P3/2 state of KrII populated in resonant Auger transitions from 3d95p/6p photo-excited states was measured at BESSY II for photon energies between 90.8 eV and 92.9 eV. The (1D)5p2P3/2 satellite was populated in the Raman regime, i.e. with a bandwidth of the exciting photons (10 meV) smaller than the natural width of the 3d95p/6p states. Partial cross sections determined from the measurement of the orientation O10 and alignment A20 are compared with results of calculations where the non-resonant part of the photoionization cross section is computed within the sudden approximation. The electron partial wave analysis as the main intention of this investigation shows that this approach yields partial cross sections for the s1/2 (d5/2) waves that are larger (smaller) than the measured ones.

Interaction between doubly-excited 4p4nℓn′ℓ′ resonances in KrI

Photoionization cross sections for the 4p4(3P)5s4P5/2,3/2,1/2 satellites and 4s → el, 4p → el main lines of Kr II were measured using the photon-induced fluorescence spectroscopy in the exciting-photon energy range between 27.80 eV and 29.44 eV with extremely narrow bandwidth (1.7 meV at 28.55 eV) of the monochromatized synchrotron radiation. The observed resonances were assigned to the 4p45s(4P1/2)np and 4p45s(2P3/2)np Rydberg series on the basis of the calculations including core relaxation and interaction between many resonances and many continua. The calculation shows that the resonance structure in the photoionization channels exists due to the 4p4(1D)5s2D5/26p3/2 and 4p4(1D)5s2D3/2 6p3/2,1/2 promoter states which strongly perturb the above Rydberg series.

Cross sections for photoabsorption and 3p44s,3d satellite production at energies of the doubly excited Ar 3p4(3P)4s2P3/2,1/2 np resonances

The photoabsorption of Ar is studied experimentally and theoretically for energies between 32.5 eV and 33.0 eV. Resonant excitation and autoionization of doubly excited 3p4(3P)4s2P3/2,1/2 np Rydberg states are observed as dominant mechanism to populate doublet and quartet satellites of the 3p44s, 3d configurations. The perturbation of the Rydberg series by promoter states is reproduced by the calculations. Measured and calculated cross sections for the strong decay channels are in good agreement. A mirror behaviour of the 3s vacancy creation and the satellite production and the influence of the radiative decay of high-lying Rydberg states on the shape of a satellite threshold are manifested.

Absolute cross sections and branching ratios for the radiative decay of doubly excited helium determined by photon-induced fluorescence spectroscopy

The decay of doubly excited helium states below the N = 2 threshold, cascading radiatively over three steps, were investigated using the photon-induced fluorescence spectroscopy (PIFS) at BESSY II. Absolute cross sections as the product of the resonance excitation cross section of the doubly excited states and their fluorescence rate to decay into the singly excited 1sms(1S) and 1smd(1D) states were measured. The experiments showed that the (sp,2n+)(1P) states decay predominantly into the 1sns(1S) states, whereas the (pd,2n)(1P) states prefer to decay into the 1snd(1D) states. For the (sp,2n−)(1P) states with n = 4, 5 and 6 we observed a broad and complex decay pattern. In addition the angular distribution of the fluorescence radiation was measured. The results are in good agreement with theoretical predictions. Furthermore, the weakening of the LS coupling scheme and the mixing between singlet and triplet states in helium was confirmed by observation of the 1s6d(3D0,1,2) → 1s2p(3P0,1,2) transition on a doubly excited singlet state.