Electron-impact spectroscopy

The methods of electron impact spectroscopy and cross section measurements are discussed and compared to optical spectroscopy. A brief summary of the status of this field and the available data is given

Isotope separation using tuned laser and electron beam

The apparatus comprises means for producing an atomic beam containing the isotope of interest and other isotopes. Means are provided for producing a magnetic field traversing the path of the atomic beam of an intensity sufficient to broaden the energy domain of the various individual magnetic sublevels of the isotope of interest and having the atomic beam passing therethrough. A laser beam is produced of a frequency and polarization selected to maximize the activation of only individual magnetic sublevels of the isotope of interest with the portion of its broadened energy domain most removed from other isotopes with the stream. The laser beam is directed so as to strike the atomic beam within the magnetic field and traverse the path of the atomic beam whereby only the isotope of interest is activated by the laser beam. The apparatus further includes means for producing a collimated and high intensity beam of electrons of narrow energy distribution within the magnetic field which is aimed so as to strike the atomic beam while the atomic beam is simultaneously struck by the laser beam and at an energy level selected to ionize the activated isotope of interest but not ground state species included therewith. Deflection means are disposed in the usual manner to collect the ions

Elastic and inelastic scattering of 40 eV electrons from atomic lead

Differential and integral electron impact cross sections for elastic scattering and for the excitation of the first five states in lead have been determined at 40 eV impact energy. The cross section measurements were placed on the absolute scale by normalizing to the optical f-value of the 6p7s3P1 transition which is the upper state for the 7229 Å, 4057 Å and 3639 Å laser emissions. The integral cross sections for elastic scattering (6p2 3P0) and for the excitation of the 6p2 3P1, 6p2 3P2, 6p2 1D2, and 6p7s 3P0(+6p7s3P1) states are: 44, 0.15, 1.5, 0.05 and 8.4*10^-16 cm^2 respectively

Differences in the Angular Dependencies of Spin- and Symmetry-Forbidden Excitation Cross Sections by Low-Energy Electron Impact Spectroscopy

Optically forbidden electronic transitions can be produced by low-energy electron impact. Recent experimental investigations of helium (1-3) have shown that the differential scattering cross sections for forbidden excitations are generally enhanced relative to those for allowed ones at low incident energies and large scattering angles. We have now observed marked differences in the angular and energy dependencies of differential cross sections for various kinds of forbidden (spin, symmetry, or both) transitions in helium at low incident energies. Such differences may well provide a basis for determining the nature of optically forbidden transitions detected by electron-impact spectroscopy in other atoms and molecules

The excitation of O2 in auroras

Newly measured electron impact cross sections for excitation of the a 1 Delta g and b 1 Sigma g+ electronic states of O2 were employed to predict the absolute volume emission rates from these states under auroral conditions. A secondary electron electron flux typical of an IBC II nighttime aurora was used and the most important quenching processes were included in the calculations. The new excitation cross sections for the a 1 Delta g and b 1 Sigma g+ states are more than an order of magnitude larger than previous estimates, and lead to correspondingly greater intensities in the atmospheric and IR-atmospheric band systems. The calculated intensity ratios of the volume emission rates of 7621 A and 1.27 microns to that for 3914 A are smaller than obtained from aircraft observations and recent rocket experiments

Excitation of the W triplet Delta (U), W singlet Delta (U), B prime triplet Sigma (U) (minus), and A prime singlet Epsison (U) (minus) states of N2 by electron impact

Electron energy-loss spectra have been obtained for N2 at 20.6 eV impact energy, and scattering angles of 10-138 deg. The differential cross section for excitation of the W triplet Delta(U) state is the largest triplet-state cross section at all scattering angles, and is the largest inelastic cross section at angles greater than 70 degrees. (Author Modified Abstract

Determination of differential elastic and vibrational excitation cross sections for e-H sub 2 scattering

Elastic scattering of electrons by hydroge

Electron impact excitation of H2O

Relative differential cross sections for elastic scattering and for a number of inelastic processes corresponding to vibrational and vibronic excitation of H2O have been determined at 53, 20, and 15 eV impact energies in the 0°–90° angular range. The measurements were carried out with an instrumental resolution of about 80 meV for transitions corresponding to the following energy losses: 0.45 eV(nu1 and/or nu3); 0.90 eV (nu1+nu3); 4.5 eV [tripletstate(s)]; 7.4 eV (Ã1B1); 9.7 eV (B-tilde1A1); 9.81 eV (tripletstate); 10.00 eV [C-tilde1B1 (0,0,0)]; 10.17 eV [D-tilde1A1 (0,0,0)]; 10.38 eV [C-tilde1B1 (1,0,0)]; 10.57 eV [D-tilde1A1 (1,0,0)]; 10.76 eV [C-tilde1B1 (2,0,0)] and [D-tilde1A1 (1,1,0)]; 11.01 eV (E-tilde1B1); and 11.11 eV (F-tilde). On the basis of the angular distribution of the scattered electrons, it is suggested that the 4.5 and 9.81 eV transitions are associated with excitations of triplet states, while the angular distribution of the scattered electrons at all other energy losses indicate predominantly singlet-singlet transitions. The sharpness of the 9.81 eV transition indicates that the corresponding state has an equilibrium geometry similar to that of the ground state

Angular Dependence of Electron Impact Excitation Cross Sections of O2

The electron-impact excitation spectrum of O2 has been studied at 20 and 45 eV impact energies and at scattering angles ranging from 10° to 90°. The angular behavior of the differential scattering cross sections for excitation of the a1Deltag, b1Sigmag+, B3Sigmau– states, for the 9.97 eV ("longest" band), and the 10.29 eV ("second" band) transitions, for the broad feature at 6.1 eV energy-loss (previously assigned to the excitation of the A3Sigmau+ state), and for elastic scattering has been determined. The experimentally measured relative differential and integral cross sections for these processes have been approximately normalized to the absolute scale. The intensities of the different transitions in optical and electron-impact spectra are compared and the importance of spin-orbit coupling and exchange processes are discussed. It is found that the energy-loss feature at 6.1 eV in the electron-impact spectrum is mostly due to the excitation of the c1Sigmau– state. This new assignment is supported by the angular and energy dependence of the scattering cross section (and by the intensity pattern found in various electron impact processes)