S. Datz

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.

Investigation of the structure of Au(110) using angle resolved low energy K+ ion backscattering☆

Abstract The reconstructed Au(110) surface has been studied by angle resolved low energy ion scattering using 600 eV K + as a probe ion. The backscattered intensities and strong multiple scattering features are consistent with very low neutralization probability and indicate the relatively higher sensitivity of alkali ion compared to inert gas ion scattering. The strong dependence upon incidence azimuthal angle attests to sensitivity of the technique as a probe of surface structure. Energy distributions are obtained for the clean and annealed Au(110) surface as a function of polar and azimuthal angles of incidence and of in-plane total scattering angle. The energies and the intensities of the single and multiple scattering features are characterized. Initial analysis of the data indicates that the distorted hexagonal overlayer and the disordered missing row models are unlikely descriptions of the surface. Comparison with computer simulation results indicates that an unrelaxed missing row model is also improbable.

Alkali‐Atom—Halogen‐Molecule Reactions in Molecular Beams; The Spectator Stripping Model

Crossed‐molecular‐beam techniques have been used to study reactive collisions in some alkali‐metal—halogen systems (Cs+Br2, K+I2, K+Br2, Rb+IBr). Both the absence of rainbow scattering in elastic‐scattering distributions and the magnitude of the reactive collision yield suggest large reaction cross sections in the order of 100 A2 for all the systems studied. The position and width of the angular distributions of alkali halide product molecules indicate forward scattering in the center‐of‐mass system with recoil energies close to zero.These observations suggest a stripping mechanism for these reactions and a model, based upon the simplest possible stripping mechanism, has been proposed to explain the observations. This model, called spectator stripping, predicts the gross features of the distributions and leads to a prediction of the maximum intermolecular distance at which reaction can occur. This corresponds to a reaction cross section of approximately 100 A2.The effect of electron transfer from the alka...

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.

Crossed molecular beam study of excited atom reactions: Hg(6 3P20) with Cl2 and chlorinated methane molecules☆

Abstract Collisions of metastable Hg atoms with halogen, hydrogen and halogenated hydrocarbon molecules produce chemiluminescent and Hg(I) photon emission: Photon production cross sections and chemiluminescent energy disposal are discussed for the reaction of Hg(6 3P20) with Cl2 and the chlorinated methane molecules.

COLLISION-INDUCED VIBRATIONAL EXCITATION AND DISSOCIATION OF HYDROGEN WITH ALKALI ATOMS AND IONS FROM 2 TO 50 eV.

Inelastic energy losses for Na0, Na+, K0, and K+ backscattered from H2 and D2 have been measured. At center‐of‐mass energies below15 ∼ eV for Na and ∼ 20 eV for K, the collisions yield vibrational excitations which are compared with the one‐dimensional exact classical calculations of Secrest. The vibrational excitation in the Na+–H2 and Na0–H2 system is in excellent agreement with three‐dimensional classical calculations of Cheng and Wolfsberg. Above these energies the molecules are dissociated but the energy loss distribution of the alkali projectile remains sharp and in the case of Na–H approaches the maximum loss possible at 50 eV.

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.

Charge-changing collisions of channeled oxygen ions in gold

Abstract Oxygen ions (4–40MeV) with various charge states have been used to study the effects of channeling upon emerging charge-state distributions and to determine the effect of channeling upon the charge-changing cross sections involved. At energies above 20 MeV, no true equilibrium is observed even for pathlength of 0.6 μm in Au channels. Instead we find quasi-equilibrium for charge states up to 6 + and strongly pathlength-dependent charge functions for 7 + and 8 + injection. The data are interpreted in terms of interaction with loosely bound outer electrons in Au.

Energy loss, angular distributions and charge fractions of low energy hydrogen transmitted through thin carbon foils

Abstract The energy loss, angular distributions and charge fractions of hydrogen transmitted through thin carbon foils in the energy range 200 ≤ E ≤ 3000 eV have been measured. The values of the stopping power constant equal 4.18 ± 0.30 and 4.38 ± 0.34 (eV)1/2 cm2/μg, where the two values are the result of using the most probable final energy and the average final energy, respectively. These values agree well with the theoretical value of 4.09 (eV)1/2 cm2/μg. The measured angular distributions were narrower than those predicted by the theory of Meyer except at the highest energies and thinnest foils. The fractions of particles emerging from the foil as positive ions, f+ , and negative ions, f −, as a function of the exit energy are given by f+ (%) = 3.0 E and f− (%) = 2.3 E, where E is in keV.