The design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail. A polarization of 43±2% is produced using NEA GaAs (100). The polarization can be easily modulated without affecting other characteristics of the electron beam. The electron beam intensity depends on the intensity of the exciting radiation at 1.6 eV; beam currents of 20 μA/mW are obtained. The source is electron optically bright; the emittance phase space (energy-area-solid angle product) is 0.043 eV mm2 sr. The light optics, electron optics, and cathode preparation including the GaAs cleaning and activation to NEA are discussed in depth. The origin of the spin polarization in the photoexcitation process is reviewed and new equations describing the depolarization of photoelectrons in the emission process are derived. Quantum yield and polarization measurements for both NEA and positive electron affinity surfaces are reported. The important considerations for interfacing he polarized electron source to an experiment are illustrated by its application to polarized low energy electron diffraction (PLEED). The advantages of this spin polarization modulated electron gun for PLEED are clearly demonstrated by sample PLEED results for W(100) and ferromagnetic Ni(110). A comparison with other polarized electron sources shows that the GaAs spin polarized electron source offers many advantages for a wide range of applications.

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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.

High resolution, inelastic electron scattering data can provide new spectroscopic information on the electronic structure of polyatomic molecules. Features in the acetone energy loss spectrum from 0 to 15 eV obtained for 100 eV incident electrons correspond to vibrational, electronic discrete, and electronic continuum excitations. These data are compared with optical measurements in a wide spectral region extending from the infrared to the vacuum ultraviolet. A comprehensive interpretation of the energy loss spectra is attempted with the use of photochemical and photoelectron data, as well as quantum-chemical calculations in the literature. Three Rydberg series with quantum defects of 1.03, 0.81, and 0.315 join onto bands previously discussed in terms of transitions to valence orbitals. These series converge to an ionization limit of 9.705 eV in good agreement with previous optical determinations. Dissociative continua underlie the Rydberg region and give rise to a variety of neutral products observed in recent photolysis work. Broad features in the ionization continuum appear to correlate generally with higher ionization potentials observed by photoelectron spectroscopy. Apparent oscillator strengths derived from the energy loss data for the bands at 4.4 and 6.35 eV and for a region (9.7–11.78 eV) of the ionization continuum agree very well with the photoabsorption measurements. Integrated oscillator strengths of 0.46 below 9.7 eV and 3.93 below 15 eV were derived from the electron impact data.

Apparent oscillator-strength values for transitions in the 4 to 14 eV region in nitrous oxide have been derived from electron energy-loss measurements. Detailed comparison with photoabsorption measurements in the ultraviolet region indicates a weak transition below the 1Δ←? 1Σ+ transition at 6.8 eV not observed optically. This analysis also provides oscillator-strength values in the region between 11.5 and 12.4 eV, where no quantitative photoabsorption data are available.