PubMed Health⌕ Search

Biomedical subjects

R Dörner

Publications and source records attributed to R Dörner.

At least 19 recordsLinked to original sources
PubMed2003

Photoelectron-photoion momentum spectroscopy as a clock for chemical rearrangements: isomerization of the di-cation of acetylene to the vinylidene configuration.

We have used complete correlated momentum mapping of the photoelectron and heavy ion products from the dissociation of the di-cation of acetylene, induced by photoionizing the carbon K shell of one of the atoms, to map out the angular correlation between the electron and the axis of the target molecule. The (quasi-) symmetric decay is found to proceed through both acetylene and vinylidene configurations. By using the strongly peaked photoelectron emission to "start a clock," an upper limit of 60 fs is placed on the isomerization time from the acetylene to the vinylidene configuration.

Journal Article↗
PubMed2003

Auger electron emission from fixed-in-space CO.

We have measured the angular distribution of carbon K-Auger electrons from fixed in space, core-ionized, CO molecules in coincidence with the kinetic energy release of the C+ and O+ fragments. We find a very narrow ejection of Auger electrons in the direction of the oxygen and an oscillatory diffraction pattern. Even for similar electron energies, the angular distribution strongly depends on the symmetry of the final state.

Journal Article↗
PubMed2002

Mechanisms of photo double ionization of helium by 530 eV photons.

We have measured fully differential cross sections for photo double ionization of helium 450 eV above the threshold. We have found an extremely asymmetric energy sharing between the photoelectrons and an angular asymmetry parameter beta approximately 2 and beta approximately 0 for the fast and slow electrons, respectively. The electron angular distributions show a dominance of the shakeoff for 2 eV electrons and clear evidence of an inelastic electron-electron scattering at an electron energy of 30 eV. The data are in excellent agreement with convergent close-coupling calculations.

Journal Article↗
PubMed2002

Symmetry-dependent multielectron excitations near the C 1s ionization threshold and distortion of the shape resonance in CO(2).

Satellite bands accompanying the C 1s photoline for the CO2 molecule parallel to the electric vector of the incident radiation E are found to be more intense than those for CO2 perpendicular to E in the shape resonance region. This indicates that multielectron excitations are caused in part by the interaction of the outgoing C 1s photoelectron with the valence electrons. The photoelectron-impact valence excitations couple with the C 1s single-hole ionization and distort the shape resonance significantly. We assign the broad resonance at approximately 312 eV to a distorted Sigma(u) shape resonance.

Journal Article↗
PubMed2002

Circular dichroism in K-shell ionization from fixed-in-space CO and N2 molecules.

We have measured the angular distributions of 1s photoelectrons excited by circularly and linearly polarized light from fixed-in-space CO and N2 molecules, in the vicinity of their shape resonances. A strong circular dichroism, i.e., a strong dependence on the sense of rotation of the polarization vector of the photons, is found for both molecules. State-of-the-art one-electron multiple scattering and partially correlated random phase approximation calculations are in good agreement with many, but not all, aspects of the experimental data.

Journal Article↗
PubMed2001

Photoelectron diffraction mapping: molecules illuminated from within.

We demonstrate the use of a multiparticle coincidence technique to image the diffraction of an electron wave whose source is placed at a specific site in a free molecule. Core-level photoelectrons are used to illuminate the molecule from within. By measuring the vector momenta of two molecular fragments and the photoelectron, a richly structured electron diffraction pattern is obtained in a body-fixed frame of the randomly oriented molecule in the gas phase. We illustrate this technique for CO, creating a photoelectron from the C(1s) shell and scanning its energy from zero to 30 eV.

Journal Article↗
PubMed2001

Strong correlations in the He ground state momentum wave function observed in the fully differential momentum distributions for the p + He transfer ionization process.

The four-particle process of proton-helium transfer ionization has been studied using cold target recoil ion momentum spectroscopy to measure the momenta of all three particles in the final state. Most of the electrons are emitted in the H0 scattering plane and in the backward direction. The final state momentum distributions show discrete structures very different from those expected for uncorrelated capture and ionization. The measured momentum pattern is interpreted to be due to a new transfer ionization reaction channel which results from strong correlations in the initial He ground state momentum wave function.

Journal Article↗
PubMed2001

Abrupt rise of the longitudinal recoil ion momentum distribution for ionizing collisions.

We report on the experimental observation of an abrupt rise in the longitudinal momentum distribution of recoil ions created in proton helium collision. The details of this structure can be related to electrons traveling with the velocity of the projectile [electron capture to the continuum (ECC)]. The longitudinal as well as the transverse distribution of the recoil ions can be explained as a continuation of the momentum distribution from ions resulting from electron capture illustrating the smooth transition from the capture to bound states of the projectile to the ECC.

Journal Article↗
PubMed1994

Effects of glutamatergic agonists and antagonists on membrane potential and intracellular Na+ activity of leech glial and nerve cells.

The membrane potential of neuropile glial cells and Retzius neurones in the central nervous system of the leech Hirudo medicinalis was measured using electrolyte-filled single-barreled microelectrodes. Intracellular Na+ activity (aNai) was recorded with Na(+)-sensitive double-barreled microelectrodes. Bath-application of kainate, quisqualate and L-glutamate elicited concentration-dependent membrane depolarizations in both cell types as demonstrated by dose-response curves. The competitive quinoxalinedione antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the non-NMDA glutamate receptor inhibited the membrane depolarizations in neuropile glial cells completely, but in Retzius neurones only partially. These results confirm that leech neuropile glial cells have a kainate- and quisqualate-preferring non-NMDA glutamate receptor similar to that in the Retzius neurones. The initial decrease in aNai in neuropile glial cells in kainate- or quisqualate-containing solutions and the afterhyperpolarization in these glial cells and the Retzius neurones following the removal of both glutamate antagonists, were blocked in the presence of the cardiac glycoside ouabain (10(-4) M). In saline solutions containing 42.5 mM Li+ instead of Na+ the afterhyperpolarizations were blocked in neuropile glial cells and Retzius neurones. We conclude that the initial aNai changes and the afterhyperpolarization could be due to the stimulation of the electrogenic Na+/K+ pump in the glial and neuronal membranes.

6-Cyano-7-nitroquinoxaline-2,3-dione↗