Gene P. Reck

Two-photon ionization of Li2: isotopic separation and determination of IP(Li2) and De(Li+2)☆

Abstract Complete isotope separation is achieved by two-photon ionization of Li 2 by a single mode Ar + laser. With the use of two Ar + lasers, the ionization potential of Li 2 is found to be 5.174 ± 0.013 eV, and the dissociation energy D e (Li + 2 ) to be 1.274 ± 0.019 eV.

Time‐resolved emission spectra following the 193‐nm photoablation of CuO, BaO2, Y2O3, and YBa2Cu3O7−x in vacuum and oxygen

Gated diode array spectra were taken after the photoablation of CuO, BaO2, Y2O3, and YBa2Cu3O7 in vacuum and oxygen. An ArF excimer laser (193 nm) was used for photoablation. The spectra were resolved on a microsecond time scale. Emission from ions, atoms, and molecular oxides are observed and identified. Observations in the first microsecond represent phenomena produced in the primary ablation process. This emission is due primarily to high‐energy collisions of ejected atoms and ions. Later time observations reveal that excited metal oxides are formed from reactive collisions of barium and yttrium atoms with the background oxygen, when present. Such species may be responsible for improved film quality in the presence of oxygen.

Isotope fractionation in two-step photoionization of Li2

Abstract A cw argon-ion laser beam intersects a thermal-energy lithium-beam. Sequential two-photon ionization of Li 2 is observed. Li + 2 ions are formed by most of the available laser lines. Large isotope fractionations result from this process.

Ionization reactions of metal hexafluorides with alkali atoms and dimers

Ionization reactions are observed in crossed beams, usually of thermal energy, of alkalis and MoF/sub 6/, WF/sub 6/, and UF/sub 6/. Previous studies have indicated large electron affinities for these hexafluorides, and this is confirmed here. Ionization at thermal energies proceeds with the alkali dimers A/sub 2/ for the three hexafluorides, but with alkali atoms A only for UF/sub 6/. Several ionization paths are observed, allowing the deduction of molecular energies. A few experiments are done with eV-range beams. Lower limits for the electron affinities are 4.5, 3.3, 4.9, 4.3, and 1.9 eV for MoF/sub 6/, MoF/sub 5/, WF/sub 6/, UF/sub 6/, and UF/sub 5/, respectively. Possible mechanisms are discussed.

Negative ions from phosphorus halides due to cesium charge exchange

An experiment has been conducted in which cesium atoms in the kinetic energy range 2–350 eV collide with phosphorus halides. Parent anions and fragments are formed. Molecular energies are obtained from threshold measurements. The electron affinites for PCl3, POCl3, PBr3, PCl2Br, PBr2Cl, and POCl2 are found to be 0.8, 1.4, 1.6, 1.5, 1.6, and 3.8 eV, respectively. The P–X bond energies for PCl3, POCl3, and PBr3 are 3.3, 3.5, and 2.6 eV, respectively.

Negative ion formation in halocarbons by charge exchange with cesium

A crossed molecular beam apparatus is used to study the formation of anions by charge exchange of fast cesium atoms with a variety of halocarbons. The branching ratios are determined from threshold to 350 eV. Comparison of the spectator stripping and information theoretical models to the data leads to the conclusion that this class of reactions is an example of an ultradirect impulsive mechanism. In the most favorable case, that of CF3I, we have determined the near threshold relative cross sections for the anions CF3I−, I−, CF−3, and IF−. From these we determine the electron affinity of CF3I− to be 1.4±0.2 eV and the bond dissociation energy of CF3‐I− as 0.38±0.1 eV, which disagrees with values obtained in a previous experiment.

Emission spectra from ArF laser ablation of high Tc superconductor Bi2CaSr2Cu2O9

A 193 nm excimer laser is used to ablate a Bi2CaSr2Cu2O9 superconductor and samples of Bi2O3, CaO, CuO, and Sr(OH)2⋅8H2O. Emission spectra generated during ablation are presented. These emissions are from simple atomic and diatomic species. Our observations show that the emission can be used to characterize the bulk material.

Negative ion formation from energetic collisions of cesium with CO2, CS2, and COS

An experiment is described in which cesium atoms, with kinetic energies in the range 10–350 eV, collide with CO2, CS2, and COS. The measured products are negative ions from charge exchange (NICE). The parent anions, CO2−, CS2−, and COS− are observed, as are other fragment ions. Intensity ratios for the various anions are measured as a function of cesium atom energy. The electron affinity of CO2, determined from crude threshold measurements, lies in the range −2.1 to −1.1 eV, with a precision of about ±0.25 eV.

Ionizing collisions of cesium with Cl2, Br2, and I2

A crossed molecular beam apparatus is used to study ionizing collisions of energetic cesium atoms with Cl2, Br2, and I2. The cross sections for formation of Cs+ are reported in the near−threshold region. The experiment combines an energy resolution better than 0.1 eV (FWHM) with a deconvolution procedure. An electron affinity of 2.50 eV is deduced for all three halogens, in good agreement with previous work. In a separate experiment, with cesium energies from threshold to 350 eV, and with much poorer energy resolution, the intensity ratios X−/X−2 are obtained. The results can be reasonably explained with an electron jump model. At energies below 30 eV, the observed ratios are in agreement with two other investigators, but between 150−350 eV they are drastically different from work reported from a third. Complementary data recently reported by a fourth group are difficult to reconcile with the present results.

Chemi‐ionization reactions of alkali dimers with halogen molecules

A crossed beam apparatus is used to characterize ionic products of thermal energy collisions of alkali dimers M2 with homonuclear halogens X2 and with IBr and ICl. All possible alkali–halogen combinations were studied, except Rb2 with ICl and IBr. When energetically possible the ionic products are mainly M+ and X−. When this path is closed two alternative paths are observed. These yield M2X+ and X−, or M+ and MX2 −. The results are discussed in the framework of a mechanism proposed by Lin, Whitehead, and Grice. The binding energy of the triatomic ions is computed with the use of an ionic model.