Stefan Klumpp

Transition probabilities from the ground state of the states of H2

The position and the intensities of the Q lines of the absorption spectrum of H2 were studied in the 81–72 nm wavelength range, using synchrotron light. The transition probabilities of the transitions with 3 ≤ n ≤ 12 have been measured and compared to calculated values. A good agreement has been found. The main discrepancies observed may well be related to local non-adiabatic couplings not included in the calculations. Vibrational couplings between levels with large Δv values up to Δv = 5 were observed affecting the transition probabilities.

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.

Photodissociation of doubly excited states of H2 into H(2s) and H(2p) fragments

The pressure dependence study of the decay of the Lyman-α fluorescence induced by the dissociation of the doubly excited states enables us to determine the 2s-to-2p dissociation channel cross section ratio, and the cross sections of each dissociation channel. Evidence of new dissociations was obtained: the Q11Σ(2) state dissociates into H(2s) + H(1s) and the Q3 states into H(2s) + H(nλ).

Observation of the oscillating absorption spectrum of a double-well state: the state of H2

The absorption spectrum of a double-well state, the state of H2, has been computed and compared with new experimental spectra in the energy range around its dissociation limit. Above the potential barrier, it is shown that the vibronic levels unexpectedly preserve a character linked to a definite well even if this character (the absorption probability) is partly shared by the neighbouring levels. The dissociation cross section presents beat-like oscillations at two frequencies as related to the classical oscillators of the two wells. The agreement with a measured high-resolution spectrum is excellent.The absorption spectrum of a double-well state, the state of H2, has been computed and compared with new experimental spectra in the energy range around its dissociation limit. Above the potential barrier, it is shown that the vibronic levels unexpectedly preserve a character linked to a definite well even if this character (the absorption probability) is partly shared by the neighbouring levels. The dissociation cross section presents beat-like oscillations at two frequencies as related to the classical oscillators of the two wells. The agreement with a measured high-resolution spectrum is excellent.

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.

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.

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.