B. P. Mathur

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.

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.

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.

Negative gaseous ions from nitric acid

A crossed‐beam system of Cs atoms and HNO3 molecules has been used to study the ion chemistry of HNO3. The existence of an HNO2− anion was observed and EA(HNO3) and D(H–ONO2−), the electron affinity of HNO3, and the dissociation energy of the parent anion were measured. Also, value for EA(NO3) was deduced which requires additional thermodynamic data and compare it with previous work. (AIP)

Calculated transitions in Li2 isotopes at argon laser frequencies

Recent spectroscopic studies of lithium dimers have been conducted with high precision. Based on these results we have determined the isotopic shift in the term energy for the B1Πu–X1Σ+g transition. Also, discrepancies with other work have come to light and are noted.

Near-threshold ionization of excited Na(32P) by collisions with O2 and SO2

Abstract Positive ions are produced in crossed beams of eV-range sodium atoms and thermal O2 or SO2. Resonant laser light is used to excite a small fraction of the sodium to Na*(3 2P 1 2 or 3 2P( 3 2 ). Product ions are observed at lower reagent kinetic energies with Na* than with Na.

Chemi‐ionization in thermal energy collisions of K2 and Cs2 with halogen molecules

Chemi‐ionization studies were conducted for K2 and Cs2 colliding with Cl2, Br2, I2 and ICl at thermal energies. (AIP)