Y.K. Bae

Production and stability of multiply charged C60 and C70 fullerene ions

Abstract The stability of multiply charged C 60 and C 70 fullerene ions has been investigated through studies of charge transfer reactions with Cs at 1–2 keV energies. A simple electron impact ion source is used to produce surprisingly intense beams of C 2+ 60 , C 2+ 70 , C 3+ 60 , C 3+ 70 , and C 4+ 60 . Fragmentation of C 3+ 60 and C 4+ 60 following successive charge transfer reactions is observed by (energy/charge) analysis of the product ions. The usefulness of producing internally excited C 60 ions via electron capture from Cs is demonstrated. The results indicate that the lifetime of C n + 60 against metastable decomposition is on the order of 10–100 μs for internal energies of 30–35 eV. The stability of C 4+ 60 against Coulomb explosion is discussed.

Magnetic bottle electron spectrometer using permanent magnets

Design principles and initial results are presented for a magnetic bottle electron spectrometer of high collection efficiency (2π sr) and good energy resolution. The instrument duplicates the carefully shaped axially decreasing magnetic field configuration of Kruit and Read [J. Phys. E 16, 313 (1983)], but replaces the high‐field electromagnet central to the Kruit–Read design with two simple pole pieces energized by permanent magnets. The use of permanent magnets requires modifications of the transition region (between the high‐field electron production zone and the low‐field drift tube analyzer) to avoid axial field reversals associated with fringing fields.

Observation of high-lying vibrational predissociation states of H+5

Abstract A photodissociation spectrum of H + 5 between 5400 and 10000 cm −1 has been measured by monitoring the H + 3 photofragment yield. Four new bands have been observed at 6690, 7130, 7490, and 7770 cm −1 , and they are interpreted to be vibrational predissociation bands resulted from excited 2ν 2 , ν 1 + ν 2 , 2ν 1 and 2ν 1 + ν 8 modes of H + 5 . The observed bands are broad; their rotational structures were not resolved by the 1 cm −1 linewidth of the laser. Combining the results of this work with those of Okumura et al., we have obtained harmonic frequencies and anharmonicity constants of the v 1 and v 2 bands: ω 1 = 4400 cm −1 , ω 2 = 4060 cm −1 , x 11 = −170 cm −1 , x 22 = −190 cm −1 , and x 12 = −310 cm −1 . Comparison of these results with the available theoretical results is given.

Observation of shell structures in the growth of microcluster ions

Abstract We have observed shell structure manifested in the size distributions of various non-metallic cluster ions sequentially grown on seed positive ions generated by electron impact ionization in a pulsed supersonic jet. The data suggest the identification of the core ion and the placement of equivalent ligands about the core during the embryonic stages of cluster growth. A crown structure similar to that of H3+·(H2)n, is indicated for H3O+·(H2)n (n⪕4). Pentagonal bipyramid structures with five neutrals surrounding a dimer ion core are suggested by the (CO)n+ (n⪕19) and (N2)n+ (n⪕14) cluster size distributions, whereas (CO2)n+ (n⪕ 16) clusters appear to have a relatively amorphous structure. Variations in the cluster size distributions of Xen+ (n⪕26) are correlated with the elongated icosahedral structure.

A high intensity cluster ion source for fast beam experiments

A high intensity cluster ion source that can be used for various fast beam spectroscopic studies has been constructed and demonstrated. The cluster ions are grown around seed ions that are generated by electron impact ionization of gas very near the exit of the nozzle (∼1 nozzle diameter distance). The generated cluster ions are coaxially focused and extracted from the pulsed (10 Hz, 200 μs pulse) supersonic expansion through a skimmer by applying a weak (∼1 V/cm) electric field, and injected into a photofragment spectrometer. With the source we have successfully generated well‐collimated intense beams of various positive and negative cluster ions, such as H+n, H3O+■ (H2)n, (CO)+n, (N2)+n, (CO2)+n, (NO)+n, He+n, Ar+n, Xe+n, and (CO2)−n, with peaks currents of ∼500 pA at cluster size n=10. Preliminary photofragmentation studies of selected cluster ions have been performed to demonstrate the capability of the source.

Shock-wave impact fusion with cluster beams

Abstract A theoretical model is presented for shock-wave cluster impact fusion that can explain and predict DD fusion rates for D 2 O, H 2 O, and D cluster beams impacting on deuterated targets, e.g. TiD, (C 2 D 4 ) n , and ZrD 1.65 . Two physically reasonable parameters, obtained from one set of data, are used as input in the general theory to provide predictions for different targets and projectiles. This theory in the form of a universal scaling equation explains and reproduces the observed fusion rates as a function of cluster beam composition and energy.

Observation of metastable autodetaching states of OH

Abstract Autodetachment has been observed in OH − ions that were produced from an H 2 O + beam traversing a Cs vapor target, with lifetimes exceeding 10 −5 s. Subsequent measurements of two types led to the conclusion that the cause is vibrationally induced autodetachment from excited v″ levels of the OH − electronic ground state. Approximate vibrational autodetachment rates for this non-Born-Oppenheimer process were calculated and found to vary from 24 to O.2 μs between v″ = 5 and v″ = 8. The present observations are consistent with a previous, but different observation by Doverspike, Champion, and Lam.

Hot plasma shock‐wave theory of cluster‐impact fusion

This paper demonstrates that cluster‐impact fusion can be understood as ‘‘hot fusion’’ on a microscopically small atomic scale. We show that it is improbable to account for the data as an artifact of contamination. By means of theoretical analysis based on a universal scaling equation, our high temperature model is shown to be consistent with the known data of recent deuteron‐deuteron fusion experiments in which clusters of D2O, H2O, and D are accelerated onto deuterated targets. Furthermore, we show that the line broadening of the experimentally obtained proton spectrum supports our prediction of the high temperature in the impact region. Although we have focused on a temperature enhancing shock‐wave model, our methodology and scaling equation are sufficiently general to encompass additional processes such as pinch instability heating. We estimate the present efficiency of this process, and predict higher efficiencies for various experimental conditions.

Comment on “An experimental and theoretical study of the negatively charged helium dimer, He2−”

Abstract It is shown that the study of the negatively charged helium dimer reported by Krishnamurthy and Mathur contains serious errors in both the theoretical interpretation and experimental analysis of this ion.