Rainer Hentges

Isotope-induced partial localization of core electrons in the homonuclear molecule N2

Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction (‘gerade’ and ‘ungerade’) are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N2 through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species—a phenomenon analogous to the acquisition of partial ‘which-way’ information in macroscopic double-slit experiments.

Photoelectron recapture observed via second-step Auger decay

Electron spectra of second-step Auger decay were taken in small steps in the vicinity of the Ne 1s → np resonances and in the near threshold regime. The spectra reveal that above the K-shell ionization limit energetically forbidden second-step Auger decay has still considerable intensity. We attribute this intensity to a recapture process of the primary photoelectron into unoccupied states and subsequent emission of a valence electron via second-step or cascade Auger decay. It is to our knowledge the first observation of delayed cascade Auger post collision interaction.

Energy and angle resolved studies of double photo-ionization of helium by electron time-of-flight coincidence spectroscopy

Helium double photo-ionization is studied by a novel coincidence technique which employs time-of-flight spectrometers. Using this technique it is possible to collect simultaneously all the electron pairs, with different energy sharing, emitted by the absorption of a single energetic incident photon. The measurements, in a configuration where the two electrons emerge at relative angle, provide the more complete information on the contribution of the ungerade amplitude to the triple differential cross section and allow the establishment of a relative scale for the full coincident angular distribution measured by other experiments at the same photon energies, but only for a few selected energy-sharing conditions.

Absorption of circularly polarized VUV radiation in polarized iron vapor.

The effect of magnetic dichroism on the total ion yield of iron, i.e. in the absorption of polarized iron vapour, was observed for the first time far away from the threshold or autoionizing states. These observations can be explained by the orientation of orbital angular momentum of the 3d-electrons. This effect has not yet been observed in the absorption measurements of magnetized iron films due to the smallness of the expectation value of the orbital angular momentum in the solid targets. The details of the dynamical behaviour go beyond single-electron approximations.

Partial photoionization cross sections of doubly excited helium below the ionization thresholds I8 and I9

In one embodiment, a network device starts a deferred discovery that defers to a prescribed transmission operation in response to detecting a message is from an identified higher device that is closer to a root of a network topology in a data network. The prescribed transmission operation and the deferred discovery each require a corresponding network device to wait at least a first half of a selected minimum contention interval before attempting transmission at a randomized position within a second half of the selected minimum contention interval. The minimum contention interval of the deferred discovery is at least twice the selected minimum contention interval. The network device transmits an updated message during the deferred discovery only if, upon reaching the corresponding randomized position of the deferred discovery, the subsequent messages from identified higher devices are less than a prescribed redundancy constant.

Coherent localization exhibited by unequal Auger Doppler components.

If coherent superpositions such as the symmetry eigenstates gerade and ungerade are in turn coherently superimposed, localization occurs. This effect is studied by the intensities of the Doppler components of electrons emitted from dissociating fragments of superexcited O2. The measurements show clear evidence for such coherent localization.