Aron Kuppermann

Determination of Electronic Energy Levels of Molecules by Low‐Energy Electron Impact Spectroscopy

This paper describes a new spectroscopic tool in nwhich optically forbidden electronic transitions can nusually be detected as clearly as optically allowed ones nin a fairly routine manner. It uses the inelastic scattering of low-energy electrons by molecules as the nmeans for determining their electronic energy levels.

Diffusion Kinetics in Radiation Chemistry. I. Generalized Formulation and Criticism of Diffusion Model

A generalized formulation of the diffusion‐kinetic model of track effects in radiation chemistry is presented and criticized. It permits consideration of complex mechanisms, arbitrary initial distributions and radical correlation effects. Methods for the numerical integration of the associated differential equations on high‐speed electronic digital computers are given and their accuracy is examined. Several applications are suggested.

Diffusion Kinetics in Radiation Chemistry. II. One-Radical-One-Solute Model; Calculations

The general diffusion‐kinetic equations are applied to a one‐radical‐one‐solute model of the radiolysis of dilute aqueous solutions. The validity of the prescribed diffusion approximation is examined. Results of calculations of the effect on the molecular and radical yields of the following parameters are given: solute concentration, solute depletion, shape of initial radical distribution, radical density, diffusion coefficients, and rate constants. Conditions under which a straight track of equal and equidistant spherical spurs can be replaced by either isolated spherical spurs or an axially homogeneous cylindrical track are examined.

Differences between Low‐Energy Electron‐Impact Spectra at 0° and at Large Scattering Angle

The preceding Comment reports some low-energy nelectron-impact spectra of helium and ethylene, obtained by a very elegant technique, which are markedly ndifferent from the ones we obtained n1 nunder other experimental conditions. It is quite important to try to nunderstand the reasons for the differences observed. nThese differences are essentially the following: (a) In nour impact spectra of helium obtained with 50-eV nelectrons we observe pronounced peaks corresponding nto the 2 ^3S state and to ionization whereas Simpson nand Mielczarek do not. (b) In our spectra of ethylene nat this same incident electron energy we observe two npronounced optically forbidden transitions and

Nonmolecular Nature of Nitric‐Oxide‐Inhibited Thermal Decomposition of n‐Butane

The thermal decomposition of most organic molecules is generally accepted to occur at least in part via a free radical chain process. Since Hinshelwood and Staveley (1) discovered that small additions of nitric oxide reduced the rate of thermal decomposition, there has been much controversy (2) concerning the nature of the “residual” reaction remaining after further additions of inhibitor produce no further decrease in rate. Jach, Stubbs, and Hinshelwood (3) have shown this limiting rate to be independent of the inhibitor used and attribute this residual reaction to a nonchain molecular process in which the parent molecule breaks up, in a single step, into stable products.

Quantum‐Mechanical Calculation of One‐Electron Properties. I. General Formulation

For a one‐electron operator, general formulas for weighted transition functions, weighted density functions, and their integrals are introduced. A detailed treatment is given of the expressions that are obtained from these formulas when they are applied to a system whose wave functions are expanded in a series of determinants of one‐electron spin orbitals. Explicit consideration is given to the nonorthogonality problem and a method for the exact inclusion of overlap terms is formulated. The simplifications resulting from the use of the single determinant approximation and orthonormal functions are discussed. A brief evaluation of the suitability of the formulation for digital computer calculation is given.

Dynamics of reaction of monoenergetic atoms in a thermal gas

When monoenergetic atoms are continuously introduced into a thermal gas, they can undergo deactivating, activating, and reactive collisions. The net result of such collisions is to establish a steady-state distribution of laboratory energies which, although not as sharp as the initial distribution, preserves some of its features, such as being centred at about the initial energy. The reactive collisions which occur under these conditions are characterized by the associated relative energy distribution function and the energy-dependent reaction cross section. As a result, as the initial laboratory energy of the atoms is experimentally varied, the relative energy distribution function can be made to sample appropriately the reaction cross section curve. Therefore, from measurements of the competition between reaction and thermalization processes as a function of initial atom laboratory energies, and from a knowledge of the non-reactive differential scattering cross section, it is possible to obtain information about the dependence on relative energy of the rotationally averaged reaction cross section. The appropriate Boltzmann steady-state equation needed to obtain this information is derived in this paper and solved for an assumed set of reactive and non-reactive cross sections. Distribution functions of relative energies are thereby obtained and used to indicate the usefulness of the suggested measurements.

The Quantum-mechanical Calculation of One-electron Properties

Two-center moment integrals for SLATER-type atomic orbitals are explicitly expressed in terms of a general formula involving the three quantum numbers and the effective nuclear charge of each of the two orbitals, the internuclear distance, and the usual A and B functions. A corresponding expression for one-center moment integrals is also given. The use of the one- and two-center moment integral formulae in digital computer calculations is discussed.