T.J. Kvale

Measurement of the electron affinity of lanthanum

The electron affinity of lanthanum has been measured using laser photoelectron energy spectroscopy. This is the first electron affinity measurement for lanthanum and one of the first measurements of an electron affinity of a rare-earth series element. The electron affinity of lanthanum was measured to be . At least one bound excited state of was also observed in the photoelectron spectra, and the binding energy relative to the ground state of lanthanum was measured as . The present experimental measurements are compared to a recent calculation.

The Toledo heavy ion accelerator

Abstract The recently installed 330 kV electrostatic positive ion accelerator at the University of Toledo is described. Experiments have been performed using ions ranging from H + to Hg 2+ and exotic molecules such as HeH + . Most of these experiments involve the beam-foil studies of the lifetimes of excited atomic states and the apparatus used for these experiments is also described. Another beamline is available for ion-implantation. The Toledo heavy ion accelerator facility welcomes outside users.

Production, Characterization, and Measurement of H(D) Beams on the ORNL Merged‐Beams Experiment

Total cross section measurements of electron capture processes are being studied for low‐energy, Aq++H(D) collisions using the Ion‐Atom Merged‐Beams apparatus at the Multicharged Ion Research Facility (MIRF) at Oak Ridge National Laboratory (ORNL). On this apparatus, a modified Faraday cup detector is used to measure the intensity of the neutral beam. The conversion of the measured electrical current to the true neutral particle beam current is necessary to accurately determine the true cross section values. Inherent in this conversion process is the number of secondary electrons (γ) emitted from the surface of the detector upon impact of an atom. The method employed to determine γ and its role in the absolute electron capture measurements at ORNL‐MIRF are presented. With a recent upgrade to the apparatus, the neutral beam H(D) production technique has been improved and is discussed in detail in this paper.

Isotope Effects in Low Energy Ion‐Atom Collisions

Isotope effects for charge transfer processes have recently received increased attention. The ion‐atom merged‐beams apparatus at Oak Ridge National Laboratory is used to measure charge transfer for low energy collisions of multi‐charged ions with H and D and is therefore well suited to investigate isotope effects. The apparatus has been relocated and upgraded to accept high velocity beams from the 250 kV High Voltage Platform at the Multi‐Charged Ion Research Facility. The intense higher velocity multi‐charged ion beams allow, for the first time, measurements with both H and D from keV/u down to meV/u collision energies in the center‐of‐mass frame. When charge transfer occurs at relatively large inter‐nuclear distances (via radial couplings) the ion‐induced dipole attraction can lead to trajectory effects, causing differences in the charge transfer cross sections for H and D. A strong isotope effect (nearly a factor of two) has been observed in the cross section for Si4++H(D) below 0.1 eV/u. However, litt...

Photoelectron angular distribution measurements of at visible wavelengths

Photoelectron angular distributions for the laser photodetachment process have been measured at six wavelengths in the region 457.9 - 647.1 nm. An intense 10 keV beam was produced in a caesium sputter-type ion source and mass-selected with a bending magnet. The mass-selected ion beam was subsequently crossed at with a linearly polarized, continuous photon beam. Angular distributions were obtained by measuring the laboratory-frame energy spectra of photodetached electrons as a function of the angle between the velocity vector of the ejected electrons and the polarization direction of the linearly polarized photon beam. The photoelectron angular distributions were used to determine asymmetry parameters. The present measurements are in excellent agreement with those of Hall and Siegel at 488.0 and 514.5 nm (1968 J. Chem. Phys. 48 943), and good agreement with a calculation by Cooper and Zare (1968 J. Chem. Phys. 48 942). The photodetachment asymmetry parameters for are compared with a recent measurement of the photodetachment asymmetry parameters for .

Electron detachment in hydrogen negative ion-atom and molecule collisions

This paper summarizes the recent measurements of single electron detachment (SED) and double electron detachment (DED) processes for 5–50 keV H− ions incident on noble gases and for 10–50 keV H− ions incident on CH4 molecules which were conducted in this laboratory. In addition to the detachment cross section measurements, the scattered beam growth curves yielded information about other charge–changing cross sections in the hydrogen–atom (molecule) collision systems.

Secondary emission yields for 3–50 keV H° atoms striking a copper target

Abstract By measuring the fractions of all three charged particles (H − , H + , and H 0 ) emerging from energetic (3–50 keV) collisions of H − ions with helium atoms, the absolute secondary negative particle emission yields γ have been determined for H 0 atoms striking a copper surface at an angle of incidence of 30° relative to the normal to the copper surface. The measured secondary emission yields monotonically increase from a value of 1.6 negative particles per atom at an incident energy of 3 keV to a value of 4.0 negative particles per atom at an incident energy of 50 keV. The impact energy dependence of the yield γ is found to be similar to the energy dependence of the yield γ exhibited by the data of previous investigators, which were obtained at projectile angles of incidence different from 30°.