Two techniques have been used to study low energy electron scattering processes in the alkali metals. A transmission experiment was used to search for resonance structure in the total scattering cross section of sodium, potassium, rubidium, and cesium. A shape resonance was observed in sodium at 0.08 (+OR-) 0.03 eV. In rubidium, evidence was found for the existence of a shape resonance below 0.05 eV. No shape resonance structure was observed in potassium or cesium for energies above 0.1 eV. For energies near the first excited state to near the lowest ionization potential, a progression of Feshbach resonances was observed in each atom. The graphical analysis technique of Spence was used to group most of these resonances into seven families. An analysis is given of the mechanisms affecting the rejection of scattered electrons in the transmission spectrometer. A quantitative description of two modes of operation of the spectrometer is presented. The second portion of this dissertation concerns the measurement of the near-threshold excitation and ionization cross sections in sodium, potassium, and rubidium. A trapped-electron experiment was used to make a relative measurement of these cross sections. The shapes of the excitation cross sections are, in general, somewhat different from other experimental work but are in good agreement with the close-coupling calculations of Moores and Norcross. The shapes of the ionization cross sections are in reasonable agreement with previous work. The ratio of the excitation cross section at 2.5 eV in sodium, 2.0 eV in potassium, and 1.8 eV in rubidium to the respective ionization cross section at the first peak was measured and found to be 3.9 (+OR-) 13% in Na, 5.8 (+OR-) 10% in K, and 6.4 (+OR-) 13% in Rb. These ratios are generally larger than those derived from independent values of the individual cross sections. An analysis of several systematic effects associated with the measurement of the cross section ratio was made. Results from this analysis were used to correct the measured excitation cross section for effects of the elastically scattered electrons.
Excitation transfer between the
62P21 and
62P23 resonance states in cesium, induced by Cs-
N2 and Cs-
H2 collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-
N2 collisions: ${Q}_{12}(^{2}P_{\frac{1}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=3.6$
A˚2, ${Q}_{21}(^{2}P_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=16.2$
A˚2, ${Q}_{10}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{1}{2}})=55.2$
A˚2, ${Q}_{20}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=63.5$
A˚2. For Cs-
H2 collisions:
Q12=6.7 A˚2,
Q21=29.6 A˚2,
Q10=11.7 A˚2,
Q20=6.7 A˚2. The large sizes of the excitation-transfer cross sections, which are comparable to the corresponding Cs-Cs cross sections, are attributed to resonances with transitions in the molecules.