[en] Photodetachment from negative ions has been studied with S^-, Cl^-, and Au^- in a static electric field. A 10 keV ion beam was sent through a region with fields of up to 1.5 kV/cm applied parallel to the beam direction. A pulsed dye laser beam perpendicular to the ion beam photodetached the ions. The cross sections were measured by detecting the resulting fast neutrals with a gated channeltron detector and a CAMAC data collection system. Below threshold detachment and oscillations on the cross section above threshold were observed near the ²P_1/2 - ³P₂S^- threshold at 16269.456 cm^-1 and near the Cl^- threshold at 29138.3 cm^-1. The amplitude of the oscillations in the s-wave data is found to be slightly reduced. Polarization dependent electric field oscillations were observed on the p-wave detachment cross section of Au^- near the threshold at 18620.2 cm^-1. Good agreement was found between the data and the theory for laser polarizations both parallel to and perpendicular to the electric field direction

[en] Photodetachment from negative ions initially bound in s-states has been studied in a static electric field. A 10 keV ion beam was sent through a region with fields of up to 1.5 kV/cm applied parallel to the beam direction. A pulsed dye laser beam perpendicular to the ion beam photodetached the ions. The cross sections were measured by detecting the resulting fast neutrals with a gated channeltron detector. Polarization dependent electric field oscillations were observed on the p-wave detachment cross section of Au^- near the threshold at 18620.2 cm^-1. A simple theory for calculating the oscillatory structure is presented. Good agreement is found between the data and the theory for laser polarizations both parallel to and perpendicular to the static electric field

[en] We have remeasured the optical oscillator strengths of eight noble-gas resonance lines in the vacuum-ultraviolet region. The measurements use a 900-eV collimated electron beam to excite the atoms, and the transmission of the emitted radiation is measured as a function of the gas density. In the method of self-absorption used here, the measured oscillator strengths are proportional to the distance between the electron beam and the fixed aperture of the spectrometer-detector system. We investigated and eliminated a possible systematic effect in the determination of the absorption length due to deflections of the electron beam. These measurements are performed at higher energies than our previous experiments at 100 eV in order to keep the electron-beam path better defined and aligned with the electron-gun apertures. The measured absolute oscillator strengths are He I (58.4 nm), 0.2700±0.0076 (2.8%); He I (53.7 nm), 0.0737±0.0023 (3.1%); Ne I (74.4 nm), 0.010 95±0.000 32 (2.9%); Ne I (73.6 nm), 0.1432±0.0038 (2.6%); Ar I (106.7 nm), 0.0580±0.0017 (2.9%); Ar I (104.8 nm), 0.2214±0.0068 (3.1%); Kr I (123.6 nm), 0.1775±0.0050 (2.8%); and Kr I (116.5 nm), 0.1416±0.0041 (2.9%)

[en] Photodetachment from negative ions initially bound in s states has been studied in a static electric field. A 10-keV ion beam was sent through a region with fields of up to 1.5 kV/cm applied parallel to the beam direction. A pulsed dye-laser beam, perpendicular to the ion beam, photodetached the ions. The relative cross sections were measured by detecting the resulting fast neutral atoms with a gated channeltron detector. Polarization-dependent electric-field oscillations were oberved on the p-wave detachment cross section of Au^- near the threshold at 18 620.2 cm^-1. A simple theory for calculating the oscillatory structure is presented. Good agreement is found between the data and the theory, for laser polarizations both parallel to and perpendicular to the static electric field

[en] The radiative efficiency of the 147 nm resonance radiation of Xe excited in a low pressure, high-frequency surface wave sustained plasma has been investigated. The radiative UV power has been obtained from optical absorption spectroscopic measurements of the Xe resonance level population and from Monte Carlo calculations of the effective decay rate of this level. Precise measurements of the rf power absorbed by the plasma enable the determination of the absolute vacuum ultraviolet discharge efficiency for the Xe surface wave discharge. Results show efficiencies up to more than 80(±11)% . copyright 1997 American Institute of Physics

No abstract available

[en] In continuation of our previous work, charge transfer processes occurring in protons on rare-gas-atom collisions have been investigated. Diagonal and real off-diagonal coherence elements of the density matrix for H(n=3) atoms produced in 20--100-keV electron-capture collisions with Kr atoms are experimentally determined by analyzing the Balmer-α light from the decay of H atoms from the (n=3) state to the (n=2) state. The intensity and polarization of the emitted light are measured as functions of an axially symmetric electric field in the collision region. These data are fitted to a numerical model of the H atom in an electric field in order to extract density-matrix elements. The results are compared to previous studies of H⁺ on He and Ar. The collisionally produced dipole moment of the H(n=3) atom decreases for increasing atomic number of the rare-gas target atoms, which indicates that the final phase of the collision process is not essential for the formation of the dipole moment. This physical picture is further supported by our alignment data. Absolute cross sections for charge transfer to the 3s, 3p, and 3d levels are presented as well

[en] Full text: We have investigated with unprecedented levels of detail, processes and phenomena involving K and L-shell photodetachment of negative ions using the high brightness, spectral resolution, and tunability of Beamline 10.0.1 on the Advanced Light Source at Lawrence Berkeley National Laboratory. In particular, we will report on recent follow-up investigations carried out in K-shell photodetachment of fundamental atomic targets such as Li^- and He^-. In the case of Li^-, preliminary results of the first detection of the neutral decay channel will be presented and compared with recent calculations. Previous work detected only positive ions produced from the photodetachment followed by Auger decay. In He^-, in addition to high resolution measurements aimed at providing a critical test of recent studies, we have also measured for the first time a simultaneous 3-electrons decay process in a negative ion. Specifically, we have measured the decay mechanism following the excitation of the triply excited state, He^- 2s2p^24Pe . This state can decay to the positive ion channel only by undergoing a simultaneous 3-electron decay (double Auger). Finally, we will also report on recent studies of photofragmentation dynamics of small negative ion clusters

[en] Highlights: ► We review recent inner-shell photodetachment measurements in anions conducted at the Advanced Light Source, Berkeley. ► Observed shape and Feshbach resonances in many species, particularly the transition metals and oxygen group elements, are summarized. ► Inner-shell threshold measurements leading to novel measurements of core-excited atomic states are described. ► The large effect of post-collision interactions in anions photodetachment is described. ► Hollow-ion state formation in the He anion is reported. -- Abstract: Inner-shell photoexcitation and photodetachment studies in strongly correlated systems are presented, with the focus on selected shape and Feshbach resonance studies, and inner-shell threshold measurements conducted on anions at the Advanced Light Source. We highlight the observations of simultaneous double-Auger decay from the He⁻2s2p²⁴P hollow ion state and the formation of shape and Feshbach resonances when filling a vacancy in the valence shell with a core electron in oxygen-group elements and transition metal anions. Measurements of inner-shell thresholds have also led to the first measurements of core-excited neutral states in a number of species.

[en] 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