Biomedical subjects

J D Bozek

Publications and source records attributed to J D Bozek.

8 recordsLinked to original sources

PubMed2005

Inner-shell photodetachment thresholds: unexpected long-range validity of the Wigner law.

Threshold behavior in inner-shell photodetachment is studied for the first time, specifically with 2-, 3-, or 4-electron emission from He- and S-. The threshold shapes are surprisingly consistent with the Wigner threshold law in all cases, despite large PCI effects observed in He-. In S-, the s-wave law is observed to agree with the data over an unprecedented range, more than an order of magnitude greater than predictions, and allows for the observation of the d-wave component. The measurements also demonstrate a means for obtaining precise core-excitation energies of free atoms.

Journal Article↗

PubMed2004

Photoexcitation of He- hollow-ion resonances: observation of the 2s2p2 4P state.

Highly correlated states are studied in He-, a fundamental 3-electron system and prototypical negative ion. The 2s2p(2) 4P state is observed for the first time. This state is detected in a resonant simultaneous double-Auger decay of unprecedented strength. In addition, the first measurements of photodetachment cross sections, positions, widths, and shapes of triply excited resonances in He- are reported. These measurements provide a sensitive test for several sophisticated ab initio calculations, and indicate differences in the position and shape of some structures.

Journal Article↗

PubMed2004

Probing the molecular environment using spin-resolved photoelectron spectroscopy.

Angle- and spin-resolved photoelectron spectroscopy with linearly and circularly polarized synchrotron radiation were used to study the electronic structure of model triatomic molecules, hydrogen sulfide, and carbonyl sulfide. The spin-polarization measurements of the molecular field split components of the S 2p photolines revealed a strong effect of the different molecular environments. The validity of simple atomic models to explain the results is discussed.

Journal Article↗

PubMed2002

Experimental evidence of a dynamic Jahn-Teller effect in C60(+).

Detailed analysis of the highest occupied molecular orbital band shape in the photoelectron spectrum of gaseous C60 reveals a dynamic Jahn-Teller effect in the ground state of C60(+). The direct observation of three tunneling states asserts a D(3d) geometry for the isolated cation, originating from a strong vibronic coupling. These results show that the ionic motion plays an important role in the electron-phonon interaction.

Journal Article↗

PubMed2002

K-shell photodetachment of He- : experiment and theory.

High-resolution K-shell photodetachment measurements of He- giving rise to He+ ions have been performed using a merged synchrotron vacuum ultraviolet photon-ion beam technique. The measurements on this fundamental negative ion display dramatic structure differing substantially, qualitatively and quantitatively, from the corresponding process in neutral atoms and positive ions, owing to the dominance of correlation in both initial and final states of He-. In addition, this experimental investigation provides an unambiguous test of two independent theoretical calculations that report serious discrepancies and shows excellent agreement with one of them.

Journal Article↗

PubMed2001

K-shell photodetachment of Li(-): experiment and theory.

An experimental K-shell photodetachment study of Li(-) giving rise to doubly photoionized Li(+) ions has been carried out at the Advanced Light Source, using a collinear photon-ion beam apparatus. The experiment reveals dramatic structure, differing substantially both qualitatively and quantitatively from the corresponding processes above the 1s ionization threshold in Li and Li(+), as predicted by our enhanced R-matrix calculation. The experimental/theoretical comparison shows good agreement over some of the photon energy range, and also reveals some puzzling discrepancies.

Journal Article↗

PubMed2001

Photoionization of metastable O+ ions: experiment and theory.

High-resolution absolute experimental measurements and two independent theoretical calculations were performed for photoionization of O+ ions from the 2P(o) and 2D(o) metastable levels and from the 4S(o) ground state in the photon energy range 30-35.5 eV. This is believed to be the first comparison of experiment and theory to be reported for photoionization from metastable states of ions. While there is correspondence between the predicted and measured positions and relative strengths of the resonances, the cross-section magnitudes and fine structure are sensitive to the choice of basis states.

Journal Article↗

PubMed2001

Chemical insights from high-resolution X-ray photoelectron spectroscopy and ab initio theory: propyne, trifluoropropyne, and ethynylsulfur pentafluoride.

High-resolution carbon 1s photoelectron spectroscopy of propyne (HC triple bond CCH3) shows a spectrum in which the contributions from the three chemically inequivalent carbons are clearly resolved and marked by distinct vibrational structure. This structure is well accounted for by ab initio theory. For 3,3,3-trifluoropropyne (HC triple bond CCF3) and ethynylsulfur pentafluoride (HC triple bond CSF5), the ethynyl carbons show only a broad structure and have energies that differ only slightly from one another. The core-ionization energies can be qualitatively understood in terms of conventional resonance structures; the vibrational broadening for the fluorinated compounds can be understood in terms of the effects of the electronegative fluorines on the charge distribution. Combining the experimental results with gas-phase acidities and with ab initio calculations provides insights into the effects of initial-state charge distribution and final-state charge redistribution on ionization energies and acidities. In particular, these considerations make it possible to understand the apparent paradox that SF5 and CF3 have much larger electronegativity effects on acidity than they have on carbon 1s ionization energies.

Journal Article↗