Walter Williams

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 (A1B1); 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.

Electron-impact cross sections for Cu atoms

Relative differential electron-impact cross sections have been measured for elastic scattering for excitation of the 3d104p 2 P1/2,3/2, 3d94s2 2D5/2 and 3d94s2 2D3/2 states of Cu at 6, 10, 20, 60 and 100 eV in the 0 degrees to 140 degrees angular range. The relative values were normalised to the absolute scale by utilising He as a secondary standard for determining the correct energy dependence and by accepting the value of the calculated elastic differential cross section at 100 eV, 40 degrees as 1.28*10-16 cm2 sr-1. Integral and momentum-transfer cross sections have been obtained by extrapolation to 180 degress. The cross section for the excitation of the 2P state is large compared to that for elastic scattering, and population inversion in this state with respect to the 2D state is readily achieved by electron impact. None of the theoretical predictions utilising classical, Born or static-exchange approximations agree with the experimental results at low impact energies.

Detection and identification of triplet states of H2O by electron impact

It has been previously (1-4) that the angular behavior of the differential cross section for exciting molecular electronic states by low-energy electron impact is a useful tool in distinguishing transitions which are optically spin forbidden from those which are spin allowed. We have used this method to investigate water vapor and have detected and identified at least two singlet→triplet transitions. One is a broad feature having a maximum intensity at about 4.5 eV excitation energy and the other has a sharp minimum at 9.81 eV. The first one had been detected previously (5-10) and the triplet state character of the upper state involved has been implied (5). The second one had not previously been detected. We show that the differential cross section for both of these excitation processes have an angular dependence characteristic of singlet→triplet transitions.

Electron impact excitation of magnesium at 10, 20 and 40 eV impact energies

Normalised differential, integral and momentum-transfer cross sections for elastic scattering and for excitation of the 33P, 31P, 31D, 41S, 41P and (33D+33P) states of magnesium have been determined at 10, 20 and 40 eV impact energies. Several autoionising transitions have been observed in the 8-12 eV region of the energy-loss spectra which correlate well with optical-absorption and ejected-electron spectra.

Photoabsorption spectrum of UF6 by electron impact

The photoabsorption cross section of UF6 in the wavelength region between 206.7 nm (2.5 eV) and 43.5 nm (28.5 eV) has been derived from the UF6 electron energy loss spectra at a 5° scattering angle and at incident electron energies of 75 and 100 eV. The shape of the resulting optical spectrum agrees well with available high‐resolution photoabsorption measurements in the 400 nm (3.1 eV) to 200 nm (6.3 eV) region. Below 200 nm, where no photoabsorption data are available, there is strong absorption and appreciable structure present. Absolute values of absorption cross sections have been obtained by normalizing the present relative data to the recently measured photoabsorption value at 225.5 nm.

Electron‐impact excitation of UF6 at an electron energy of 20 eV in the energy‐loss range of 0–10 eV

Electron‐impact excitation of UF6 at low incident electron energies is reported. (AIP)Electron‐impact excitation of UF6 at low incident electron energies is reported. (AIP)

Electron Scattering by Molecules with and without Vibrational Excitation. VI. Elastic Scattering by CO at 6–80 eV

Elastic scattering differential cross sections in relative units for electron scattering from CO have been measured in the scattering angle range 15°–85° and the impact energy range 10–80 eV. The experimental results are compared to the predictions of model polarized Born approximations using five different model interaction potentials. The model potential of Crawford and Dalgarno is in the best agreement with experiment, and agrees with experiment about as well as any local potential possibly can. Such a treatment is able to account for some of the features of the angle dependence of the differential cross sections. The largest discrepancies between theory and experiment are at 10 eV and at large scattering angles, and there are also smaller discrepancies at small scattering angles. Comparisons are also made to previous experimental studies by Ramsauer and Kollath and Arnot.

Elastic and inelastic scattering of electrons by atomic manganese

Electron scattering by manganese has been studied in the 10-100 eV impact energy and 10-130 degrees angular ranges. In certain energy and angular ranges cross sections for several inelastic processes exceed those associated with elastic scattering. The angular distributions which characterise optically spin-allowed and spin-forbidden transitions involving singlet and triplet states in the case of light elements seem to apply to transitions among states of high spin multiplicity. Differential, integral and momentum-transfer cross sections for elastic scattering and excitation of the y6P, z6P, a6D, a4P, z4P and z8P states have been obtained at 20 eV impact energy. The cross sections were normalised to the absolute scale by using the optical f value of the z6P excitation.

Angular distributions in the electron impact excitation of Xe at 20 eV

Electron impact energy‐loss spectra of Xe have been studied at 20 eV incident electron energy from 5° to 135° scattering angle. Differential and integral cross sections for elastic scattering and for the excitation of electronic states up to 10.60 eV energy loss have been determined. The validity of the optical selection rules and the previously established angular behavior associated with direct and exchange processes were examined for this intermediate coupling case.

Electron impact excitation of potassium at 6.7, 16 and 60 eV

Normalized momentum-transfer cross sections and differential and integral cross sections for elastic scattering and for the excitation of the 4p2P3/2,1/2 and the (5s2S1/2 + 3d2D5/2,3/2) levels in potassium are reported. There is considerable disagreement between the present experimental results and previous optical excitation measurements and theoretical results. Autoionization features associated with the 3p inner-shell excitations, some of which have been observed previously in optical absorption and ejected-electron spectra, have been detected in the electron impact energy-loss spectrum.