Measurements of the vacuum-ultraviolet (<80-nm) radiation produced by intense ultraviolet (248-nm) irradiation (1015–1016 W/cm2) of rare gases have revealed the copious presence of both harmonic radiation and fluorescence from excited levels. The highest harmonic observed was the seventeenth (14.6 nm) in Ne, the shortest wavelength ever produced by that means. Strong fluorescence was seen from ions of Ar, Kr, and Xe, with the shortest wavelengths observed being below 12 nm. Furthermore, radiation from inner-shell excited configurations in Xe, specifically the 4d95s5p → 4d105s manifold of Xe7+ at ~17.7 nm, was detected. These experimental findings, in alliance with other studies concerning multielectron processes, give evidence for a role of electron correlations in a direct nonlinear process of inner-shell excitation.

Studies of multiphoton production of vacuum-ultraviolet radiation in the rare gases

Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4π and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.

/pdf/recoil-ion-and-electron-momentum-spectroscopy-reaction-c7ai542e3l.pdf

Recoil-ion and electron momentum spectroscopy: reaction-microscopes

The Standard Model of particle physics is known to be incomplete. Extensions to the Standard Model, such as weak-scale supersymmetry, posit the existence of new particles and interactions that are asymmetric under time reversal (T) and nearly always predict a small yet potentially measurable electron electric dipole moment (EDM), d(e), in the range of 10(-27) to 10(-30) e·cm. The EDM is an asymmetric charge distribution along the electron spin (S(→)) that is also asymmetric under T. Using the polar molecule thorium monoxide, we measured d(e) = (-2.1 ± 3.7stat ± 2.5syst) × 10(-29) e·cm. This corresponds to an upper limit of |d(e)| < 8.7 × 10(-29) e·cm with 90% confidence, an order of magnitude improvement in sensitivity relative to the previous best limit. Our result constrains T-violating physics at the TeV energy scale.

/pdf/order-of-magnitude-smaller-limit-on-the-electric-dipole-aljuwj3am0.pdf

Order of Magnitude Smaller Limit on the Electric Dipole Moment of the Electron

Cold Target Recoil Ion Momentum Spectroscopy: a &momentum microscope' to view atomic collision dynamics

This compilation revises the 1991 listing of atomic data for the lighter elements from hydrogen to gallium. The tabulation emphasizes resonance lines, i.e., lines whose lower level is the ground state, or an excited fine-structure state of the ground term, and is restricted to wavelengths longward of the H I Lyman limit at 911.753 ?. All but the very weakest known and predicted electric-dipole transitions are included, but no forbidden lines. This paper has attempted to review all data published by the end of 2002.?????The tables contain the best data available to the author on ionization potentials, level designations, vacuum and air wavelengths, lower and upper energy levels, statistical weights, transition probabilities, natural damping constants (reciprocal lifetimes), oscillator strengths, and the often used combinations of log gf and log ?f. All ion stages with relevant classified lines are included. Individual components resulting from isotope shift and hyperfine structure are listed explicitly for certain species. The accompanying text provides references, explanations for the critical selection of data, and notes indicating where new measurements or calculations are needed.?????This compilation should be particularly useful in the analysis of interstellar and quasar absorption lines and other astrophysical sites where the density of particles and radiation is low enough to excite only the lowest atomic levels. The data also are relevant to the study of stellar atmospheres, and gaseous nebulae.?????An Appendix summarizes new data relevant to the similar compilation in Paper II for the elements germanium to uranium.

https://iopscience.iop.org/article/10.1086/377639/pdf

Atomic Data for Resonance Absorption Lines. III. Wavelengths Longward of the Lyman Limit for the Elements Hydrogen to Gallium

Doubly-excited states in light atoms

Many new lines between 2 000 and 5 500 A from displaced terms in the B II spectrum are observed using the beam-foil technique. Possible transitions in the doubly-excited quartet system of B III are compared with previous observations in Be II. Other transitions in B II, B III, and B IV are also identified.

Line identifications in the beam-foil spectrum of boron.

Collinear laser--ion-beam spectroscopy has been used to measure hyperfine structure (hfs) in three levels of the 3d/sup 2/ and six levels of the 3d4p configuration of Sc II. The results combine with earlier measurements of hfs within these configurations to give a fairly complete picture of hfs in these configurations. The combined results are compared with multiconfiguration Dirac-Fock (MCDF) ab initio calculations. Good agreement is obtained for the magnetic dipole hfs constants of the singlet states in both the 3d/sup 2/ and 3d4p configurations, but the MCDF predictions for the triplet states are not even qualitatively correct. The poor agreement for the triplet states appears to be due to the neglect of core polarization in the present MCDF approach.

Hyperfine structure of Sc II: Experiment and theory

Thin carbon foil breakage times under ion beam bombardment

We describe measurements of the lifetimes of metastable states in one- and two-electron nickel ions. The 2 2 S 1/2 level in one-electron nickel was found to have a lifetime of 217.1(1.8) ps, in agreement with a theoretical calculation of 215.45 ps. The lifetimes of the 2 1 S 0 and 2 3 P 2 levels in two-electron nickel were found to be 156.1(1.6) and 70(3) ps, respectively, in agreement with the theoretical results of 154.J(0.5) and 70.6 ps. We also studied the phenomenon of hyperne quenching of the He-like 2 3 P 0 level by comparing decay curves for the isotopes 61 Ni and 58 Ni

H. G. Berry

Papers

Doubly-excited states in light atoms

Line identifications in the beam-foil spectrum of boron.

Hyperfine structure of Sc II: Experiment and theory

Thin carbon foil breakage times under ion beam bombardment

Forbidden transitions in one- and two-electron nickel.