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N Zema

Publications and source records attributed to N Zema.

7 recordsLinked to original sources
PubMed2005

Valence photoionization dynamics in circular dichroism of chiral free molecules: the methyl-oxirane.

The dynamical behavior of circular dichroism for valence photoionization processes in pure enantiomers of randomly oriented methyl-oxirane molecules has been studied by circularly polarized synchrotron radiation. Experimental results of the dichroism coefficient obtained for valence photoionization processes as a function of photon energy have been compared with theoretical values predicted by state-of-the-art ab initio density-functional theory. The circular dichroism measured at low electron kinetic energies was as large as 11%. Trends in the experimental dynamical behavior of the dichroism coefficients D(i)(omega) have been observed. Agreement between experimental and theoretical results permits unambiguous identification of the enantiomer and of the individual orbitals.

Journal Article↗
PubMed2001

Electronic and magnetic structures of Sr(2)FeMoO(6).

We have investigated the electronic and magnetic structures of Sr(2)FeMoO(6) employing site-specific direct probes, namely x-ray absorption spectroscopy with linearly and circularly polarized photons. In contrast to some previous suggestions, the results clearly establish that Fe is in the formal trivalent state in this compound. With the help of circularly polarized light, it is unambiguously shown that the moment at the Mo sites is below the limit of detection (<0.25 mu(B)), resolving a previous controversy. We also show that the decrease of the observed moment in magnetization measurements from the theoretically expected value is driven by the presence of mis-site disorder between Fe and Mo sites.

Journal Article↗
PubMed2001

Role of excitons in electron- and photon-stimulated desorption of neutrals from alkali halides.

Low-energy (5-15 eV) electron- and photon-stimulated desorption of KI(100) yields I2P3/2 and 2P1/2 with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the gamma3/2-exciton long-wavelength edge. Exciton decay at the surface directly produces I2P3/2 and 2P1/2 with hyperthermal velocity and is in competition with self-trapping. Spin memory of the gamma-exciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides.

Journal Article↗