Long-range predissociation in two-color photoassociation of ultracold Na atoms

We report two-color photo-associative ionization of sodium in a Magneto-Optical Trap. The experimental results yield information on both singly and doubly excited states. We find that the highest bound vibrational levels (v > 20) of the singly-excited 0^- g state predissociate into the 3²P3/2 + 3^²S½(Fg=1) dissociation continuum due to avoided cross- ings of the hyperfine components of this potential with other molecular symmetries. Based on symmetry and energy con- siderations we argue that a doubly-excited 1u state remains autoionizing even when excited only a few GHz above the dis- sociation continuum

New diagnostic technique for Zeeman-compensated atomic beam slowing: technique and results

We have developed a new diagnostic tool for the study of Zeeman-compensated slowing of an alkali atomic beam. Our time-of-flight technique measures the longitudinal veloc- ity distribution of the slowed atoms with a resolution below the Doppler limit of 30 cm/s. Furthermore, it can map the position and velocity distribution of atoms in either ground hyperfine level inside the solenoid without any devices inside the solenoid. The technique reveals the optical pumping ef- fects, and shows in detail how the slowing within the solenoid proceeds. We find that most atoms in the chosen hyperfine state are decelerated in the slowing process. The width of the velocity distribution is mainly determined by inhomogeneities in the slowing laser beam, and after expanding the laser beam, the width is reduced to 2.5 m/s, corresponding to 3.2 mK. Fi- nally, we discuss and show a method to produce a beam with two-velocity components for the study of head-tail low energy collisions

Vibrational state distribution of 2-Na^+ ions created in ultracold collisions

The vibrational distribution P(v) of 2-Na^+ ions created in ultracold collisions in a magneto-optical trap has been deter- mined. Only two vibrational states with v = 2 and 3 are popu- lated and we find P(2)=0.29±0.02 and P(3)=0.71±0.02. The results provide conclusive evidence that the ionization mech- anism is photo-associative autoionization,and not photo- associative photoionization and will form a fundamental test for the theoretical description of the process

Dissociative ionization of H2 and D2 by electron impact near threshold

We have studied the dissciative ionization of H2 and D2 by electron impact. It is found that in the vicinity of the 2Σ+g dissociation threshold of H+2 (18.08 eV) a significant fraction of the produced protons originates from the process e + H2 → H− + H+ + e (threshold at 17.34 eV). Similar results are found for D2

Polarization of the radiation induced by electron impact on He and Hg

The polarization of a number of He and Hg spectral lines, excited by a beam of electrons, has been measured as a function of the electron energy. The transitions studied are: for helium 41D → 21P, 51D → 21P, 43S → 23P, 33D → 23P 43D → 23P, for mercury 61D2 → 61P1, 63D2 → 61P1, 73S1 → 63P1, and 71D1 → 61P1. The electron energy was varied from the threshold energy to a few eV above it. The results indicate that in most cases the polarization measured near the threshold is much lower than the theoretically predicted threshold polarization. For some transitions a detailed structure near threshold is observed in the polarization function. The observed behaviour of the polarization near threshold is discussed and a qualitative interpretation is presented

Negative ions in electron impact excitation of He near 60 eV

An experimentally verifiable effect on the excitation cross section in helium due to the broad (2s2p2) 2Se He- state predicted by Fano and Cooper in 1965, but hitherto unidentified, and other He- states, are predicte

A new type of He- resonance states in the autoionisation region

The authors have studied the near-threshold excitation of autoionising states in electron-helium scattering. Only a particular set of autoionising states is observed in the measurements, which has led them to formulate a selection rule for threshold excitation of autoionising states. Evidence is presented that autoionising states belonging to this particular set are strongly excited near their thresholds by hitherto unknown shape resonances

Investigation of an Optical Potential Model for Post-Collision Interaction in Ejected-Electron spectra

An optical potential method is used to formulate a model for the post-collision interaction that occurs in electron-helium scattering after excitation and decay of autoionising states. The model is an extension of an earlier description given by Nienhuis and Heideman, and is used to study the effects of post-collision interaction in ejected-electron spectra. The authors present a calculation of angular distributions of ejected electrons from the He**(2s2)1S autoionising state. It is argued that study of angular momentum exchange during the post-collision interaction requires detailed knowledge of the interfering background of the direct ionisation process