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

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

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

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)

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

Elastic scattering of electrons by hydroge

Elastic electron scattering by laser-excited 138Ba( ... 6s6p 1P1) atoms

The results of a joint experimental and theoretical study concerning elastic electron scattering by laser-excited 138Ba( ... 6s6p 1P1) atoms are described. These studies demonstrate several important aspects of elastic electron collisions with coherently excited atoms, and are the first such studies. From the measurements, collision and coherence parameters, as well as cross sections associated with an atomic ensemble prepared with an arbitrary in-plane laser geometry and linear polarization (with respect to the collision frame), or equivalently with any magnetic sublevel superposition, have been obtained at 20 eV impact energy and at 10°, 15° and 20° scattering angles. The convergent close-coupling (CCC) method was used within the non-relativistic LS-coupling framework to calculate the magnetic sublevel scattering amplitudes. From these amplitudes all the parameters and cross sections at 20 eV impact energy were extracted in the full angular range in 1° steps. The experimental and theoretical results were found to be in good agreement, indicating that the CCC method can be reliably applied to elastic scattering by 138Ba( ... 6s6p 1P1) atoms, and possibly to other heavy elements when spin-orbit coupling effects are negligible. Small but significant asymmetry was observed in the cross sections for scattering to the left and to the right. It was also found that elastic electron scattering by the initially isotropic atomic ensemble resulted in the creation of significant alignment. As a byproduct of the present studies, elastic scattering cross sections for metastable 138Ba atoms were also obtained