In this review we present the energies, configuration, and other properties of resonances (also called "compound states" and "temporary negative ions") in diatomic molecules. Much of the information is presented in the form of tables and energy level diagrams. Vibrational, rotational, and electronic excitation are discussed whenever these processes have given information on resonances; often these excitation processes proceed via resonances. The paper is divided according to molecular species (${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, CO, NO, ${\mathrm{O}}_{2}$), but the main conclusions are discussed by the nature of the processes involved.

Resonances in Electron Impact on Diatomic Molecules

Field Emission Energy Distribution (FEED)

The distribution in center‐of‐mass energy caused by the thermal motion of the target gas molecules has been rigorously derived for the case of a monoenergetic particle beam interacting with target molecules having an isotropic Maxwellian velocity distribution corresponding to temperature T°K. Provided the nominal c.m. energy E0 exceeds a few kT, the distribution has a full width at half‐maximum (FWHM) of W1/2=(11.1γk T E0)1/2. where γ=m/(m+M), m and M being the projectile and target masses. This is identical to the width derived previously in a one‐dimensional approximate treatment by Bethe and Placzek. The exact and approximate distributions differ significantly, however, in shape and mean energy, particularly at low values of E0/γkT. The Doppler width, W1/2, is shown to significantly affect the appearance curve of the products of endothermic reactions involving heavy particles. Convolution integrals are derived for a number of idealized forms of the cross section for such reactions. In the extreme case ...

Doppler Broadening in Beam Experiments

Potential-energy curves for molecular hydrogen and its ions

Unique information about the motion and correlation of valence electrons in atoms, molecules and their ions is obtained from electron-impact ionization reactions near the Bethe ridge at total energies of the order of 1000 eV or higher. This is electron momentum spectroscopy. The history, theory and practice of the field are discussed and its value is shown by numerous examples.

https://iopscience.iop.org/article/10.1088/0034-4885/54/6/001/pdf

Electron momentum spectroscopy of atoms and molecules

A study has been made of all the known factors which limit the performance of high resolution (0.07 to 0.01 eV FWHM) monochromators. These limiting factors have been incorporated into design equations for the optimum (maximum current output) monochromator. The conclusions are tested by performance measurements on a prototype instrument. The results require the introduction into the design equation of a new limiting factor, an anomalous energy spread in dense electron beams, which is empirically determined.

Electron Monochromator Design

The transmission of electrons through the rare gases and mercury vapor has been examined as a function of electron energy, with energy resolution of about 0.04 eV. Many anomalies (resonances) localized in energy have been observed, totaling 11 in helium, six in neon, two each in argon and krypton, five in xenon, and 13 in mercury. The interpretation of these resonances in terms of compound negative ion formation is discussed, and in several cases electron configurations are assigned to the negative ions. In helium, neon, xenon, and mercury, sharp decreases in transmission are observed which are attributed to the onset of inelastic processes. Definite identification of the inelastic processes in the case of helium permits calibration of the absolute electron energy scale to within \ifmmode\pm\else\textpm\fi{}0.03 eV.

ELASTIC RESONANCES IN ELECTRON SCATTERING FROM He, Ne, Ar, Kr, Xe, AND Hg

The calculated performance of electrostatic analyzers of the cylindrical and spherical deflection type are compared. It is shown that considering geometrical terms through the third order the cylindrical device is significantly superior.

/pdf/comparison-of-the-spherical-deflector-and-the-cylindrical-4idcx5g98u.pdf

Comparison of the Spherical Deflector and the Cylindrical Mirror Analyzers

The photoelectron spectrum of NO2 has been measured with high resolution up to 27.5 eV and interpreted by use of molecular orbital theory, taking especially the vibrational structure into account. The electron impact energy loss spectrum has been measured with electron energy 100 eV. The spectrum above 6.5 eV has been interpreted as due to Rydberg transitions and comparison with spectroscopic measurements have been made.

https://iopscience.iop.org/article/10.1088/0031-8949/1/4/005/pdf

Rydberg series of small molecules VIII. Photoelectron spectroscopy and electron spectroscopy of NO2

It is shown that by use of a multistage technique in which electrons are drawn from a cathode by a high potential and decelerated to the required final energy, guns can be designed capable of forming beams in which the current is limited only by space charge in the beam itself. The design principles and procedures are given and illustrated by two examples of electron guns giving highly collimated beams and operating at energies of 30 and 500 eV. The measured currents obtained are somewhat greater than the space charge limited beam maximum because of ion neutralization.

C. E. Kuyatt

Papers

Electron Monochromator Design

ELASTIC RESONANCES IN ELECTRON SCATTERING FROM He, Ne, Ar, Kr, Xe, AND Hg

Comparison of the Spherical Deflector and the Cylindrical Mirror Analyzers

Rydberg series of small molecules VIII. Photoelectron spectroscopy and electron spectroscopy of NO2

Design of Low Voltage Electron Guns