Ellison H. Taylor

Study of Chemical Reaction Mechanisms with Molecular Beams. The Reaction of K with HBr

The reaction between K and HBr has been studied by a molecular beam technique, using as a detector a surface ionization gauge with a tungsten and a platinum alloy filament, the former sensitive to KBr as well as to K and the latter essentially to K only. The activation energy is 3.4±0.1 kcal/mole and the probability or steric factor is about 0.1. The angular distribution of the KBr suggests that collisions with the H end of the HBr are more often fruitful than other configurations. The total collision cross section for a beam of K at 504°K in HBr at 401°K is 850×10—16 cm2.

Ionization on Platinum and Tungsten Surfaces. I. The Alkali Metals

The ionization of all of the alkali metals on tungsten and on tungsten oxide surfaces follows the Saha‐Langmuir equation with no reflection. On platinum, however, a departure from this equation indicates partial reflection of the atoms. The reflection of Na is probably 0%, since the ionization efficiency is given closely by the Saha‐Langmuir equation with a value of 5.50 ev for the work function of Pt at 2000°K. The same value of the work function then indicates reflections of 18% for Li, 48% for K, 22% for Rb, and 8% for Cs, at 2000°K.

COLLISION MECHANICS IN CROSSED MAXWELLIAN MOLECULAR BEAMS

A general treatment of the mechanics of collision between two Maxwellian molecular beams is described. Expressions are obtained for the distribution in collision energy, for the elastic and reactive collision rates, and for the angular distribution of the center of mass vectors for beams colliding at any angle. The treatment can accommodate any reaction cross section which can be expressed as a step function multiplied by a linear combination of powers of the relative energy.The recoil momentum which affects the product distribution in the laboratory system is discussed, and the treatment is applied to some experimental data on the reaction of K with HBr.

Ionization on Platinum and Tungsten Surfaces. II. The Potassium Halides

The ionization of the potassium halides on tungsten follows the Saha‐Langmuir equation and indicates the formation of stable partial films of halide. On platinum, however, reflection occurs amounting to more than 99% for KCl, KBr, and KI, and about 75% for KF.

The Effects of Ionizing Radiation on Solid Catalysts

Publisher Summary This chapter discusses the effects of ionizing radiation on solid catalysts. The study of a catalyst by irradiation consists of four steps: (1) damage to the solid by irradiation, (2) the characterization of the defects produced, (3) the measurement of changes in catalytic activity or chemisorptions brought about by the irradiation, and (4) the attribution of any such changes to specific types of defect. Radiation has been observed to produce effects, such as alteration of surface area, desorption under radiation, and modification of physical adsorptivity. Because they show less variability from substance to substance than do catalysis and chemisorption, they are classed together as “nonspecific effects.” A special method for the irradiation of a catalyst is to incorporate in it atoms of a radioactive isotope. There is a connection between the preirradiation technique and the simultaneous irradiation of catalyst and substrate. Several adsorption experiments have been done under irradiation. Such experiments are simpler than radiolysis in the presence of a solid and helps in understanding the more complex systems.

Thermal Emission of Alkali Ion Pulses from Clean and Oxygenated Tungsten

The spontaneous emission of positive ions from a heated tungsten filament occurs as pulses, a single pulse releasing as many as 106 ions in less than 100 μsec. The pulses are composed mainly of potassium ions, present as impurities in the tungsten lattice. It is suggested that the emission of positive ions in the form of bursts is dependent upon the existence of edge dislocations in the metal. At temperatures where the formation of an adsorbed layer is possible, oxygen has a very pronounced effect upon the rate of emission of positive ion pulses.

The effect of ionizing radiations on catalytic activity. Hydrogenation and isotopic exchange on inorganic solids

Irradiation at --78 deg C with doses of Co/sup 60/ gamma rays in the range 10/sup 18/ to 10/sup 20/ ev/g increased, from three to several hundred times, the catalytic activity for hydrogendeuterium exchange of ZnO, ThO/sub 2/, BaTiO/sub 3/, MgO, V/sub 2/O/sub 3/, KAlSi/sub 3/O/sub 8/, and CaSiO/sub 3/. The catalytic activity of TiO/sub 2/ (rutile) was virtually unaffected by gamma rays at this temperature but could be increased by exposure to neutrons. The activity of several hydrides (LiH, NaH, BaH/sub 2/, CaH/sub 2/) was decreased by irradiation in vacuo, but it was increased (for the two investigated, LiH and BaH/ sub 2/) by irradiation in 20 to 30 mm of H/sub 2/. The hydrogen-deuterium exchange activity of promoted zinc oxides was virtually unchanged by irradiation, in contrast to the increase with pure ZnO. Activity for ethylene hydrogenation, however, was decreased for both promoted and unpromoted zinc oxides. (auth)

Thermal Positive Ion Emission and the Anomalous Flicker Effect

The correlation between the anomalous flicker effect in space charge limited diodes and the positive ion pulses which generate it is studied in the light of recent measurements of the size and shape of thermal positive ion pulses from tungsten filaments. It is shown that the positive ion pulses, although smaller than the electron pulses, have similar duration times, and that the periodic structure of the electron pulses may be quantitatively explained by reflection of the positive ion bursts back and forth through the region of maximum space charge.