The absolute cross section, differential in laboratory scattering angle, for the process $\rm H\sp{+} + O\to H + O\sp{+}$ using 1.5 keV-energy protons is reported. The total cross section value of (8.7 $\pm$ 1.9) $\times$ 10$\sp{-16}$ cm$\sp2$ derived from the integration of the differential cross section is compared with existing cross section data.

This thesis reports the first controlled study of the interactions of Rydberg atoms with a metal surface. In these experiments, a collimated beam of potassium Rydberg atoms is directed at a plane surface at near grazing incidence. Positive ions formed by surface ionization are attracted to the surface by their image charge, which is counterbalanced by an external electric field applied perpendicular to the surface. The ions are detected by a position-sensitive detector (PSD). At some critical value of the external field, the ion trajectories just miss the surface, suggesting that analysis of the dependence of the ion signals on external electric field can be used to determine the distance from the surface at which ionization occurs. This distance, and thus the corresponding critical electric field, is expected to be n-dependent. Experimentally, however, it was observed that the ion signal had a sudden n-independent onset when only a small positive perpendicular electric field was applied at the surface. This observation requires, surprisingly, that the ions produced by surface ionization can readily escape from the surface. The data do, however, show that Rydberg atoms are efficiently ionized in collisions with the surface. This process may provide a useful new detection technique for Rydberg atoms.

Spectroscopy of the high-lying vibrational levels of the $1\sp3\Sigma\sbsp{g}{+}$ and $1\sp1\Sigma\sbsp{u}{+}$ states of both $\rm\sp6Li\sb2$ and $\rm\sp7Li\sb2$ has been accomplished via photoassociation of ultracold atomic lithium confined in a magneto-optical trap. Both these molecular states correlate to $2S\sb{1/2}$ plus $2P\sb{1/2}$ free atomic states. The long range part of these molecular potentials depends on the 2P atomic radiative lifetime. Accurate models were constructed for both the $1\sp3\Sigma\sbsp{g}{+}$ and $1\sp1\Sigma\sbsp{u}{+}$ potentials. By fitting these models to the experimentally measured vibrational levels observed in $\rm\sp6Li\sb2$ and $\rm\sp7Li\sb2$, we have been able to extract a value for the 2P lifetime of lithium. Fitting to the absolute values of the data gives a value of 26.99 $\pm$ 0.16 ns whereas fitting to differences in the spectral features gives a value of 27.04 $\pm$ 0.18 ns. While both values agree with previous work, improvements made in the potential models would enable this analysis to resolve the current discrepancy between experiment and theory.

The major constituent in the atmosphere of the Earth at altitudes between 200 and 500km is atomic oxygen.$\sp1$ Collisions involving atomic oxygen are therefore important in this region of the atmosphere. Due to the difficulty in producing atomic oxygen in the laboratory, there are very few reported measurements of scattering cross sections with an atomic oxygen target.$\sp{2-6}$ We have undertaken an experimental program designed to measure absolute differential cross sections for various collision processes involving atomic oxygen. The oxygen atoms are produced through dissociation of O$\sb2$ in a microwave discharge, producing a target of atomic and molecular oxygen whose densities are inferred from measurements with an electron impact time of flight mass spectrometer.

Atoms moving in an intense, near resonant standing wave (SW) experience a force along the direction of the SW. This force has been investigated by observing its effect on the transverse velocities of atoms in a thermal beam. When the standing wave is tuned above resonance the atomic beam is collimated and has an increased intensity at the center of the beam. Below resonance, the SW anti-collimates the atomic beam, reducing the central intensity. These effects are due to the interaction between the induced atomic dipole and the inhomogeneous field of the SW. Further investigation shows structure in the transverse velocity distribution of the atomic beam. This structure is due to multiphoton (Doppleron) resonances in the force. Calculations reproduce the dipole force and multiphoton resonance effects and are in good agreement with the data.

Absolute partial cross sections from threshold to 1000 eV are reported for electron-impact ionization of Ar, H$\sb2$, N$\sb2$, O$\sb2$, and CO$\sb2$. Data are presented for the production of Ar$\sp{n+}\ (n=1{-}4)$ from Ar; the production of H$\sbsp{2}{+}$ and H$\sp+$ from H$\sb2$; the production of N$\sbsp{2}{+},\ \rm N\sp{+}+N\sbsp{2}{2+}$, and N$\sp{2+}$ from N$\sb2$; the production of O$\sbsp{2}{+}$, $\rm O\sp{+}+O\sbsp{2}{2+}$, and O$\sp{2+}$ from O$\sb2$; and the production of CO$\sbsp{2}{+}$, CO$\sp{+}$, CO$\sbsp{2}{2+},$ O$\sp{+}$, C$\sp{+}$, O$\sp{2+}$, and C$\sp{2+}$ from CO$\sb2$. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output provides a clear demonstration of the complete collection of energetic fragment ions from dissociative ionization. For singly charged parent ions, the overall uncertainty in the absolute value of the cross sections reported here is $\pm$3.5% and is marginally higher for multiple and dissociative ionization. Previous cross section measurements are compared to the present results. Additionally, combining the flight time and detection location of fragment ions yields some qualitative information about their energy distribution.

A semiclassical model of Rydberg atom collisions with neutral molecules that result in electron attachment has been devised and implemented as a Monte Carlo computer program. Comparisons between model calculations and experimental data have been used to investigate the reactions:$$\eqalign{&{\rm K}(n{\rm d})+{\rm SF}\sb6\to{\rm K}\sp{+}+{\rm SF}\sb6\sp{-*},\cr&{\rm K}(n{\rm d})+\rm CF\sb3I\to K\sp{+}+CF\sb3I\sp{-*}\to K\sp{+}+CF\sb3+I\sp-,\cr&{\rm K}(n{\rm d})+\rm CCl\sb4\to K\sp{+}+CCl\sb4\sp{-*}\to K\sp{+}+CCl\sb3+Cl\sp-.}$$These comparisons provide information about the distribution of excess energy of reaction between internal and translational degrees of freedom and about the lifetimes of the intermediate negative ions, forming the basis of one of the few techniques that can be used to measure lifetimes of collisionally produced excited species on a picosecond time scale.

The response of rubidium Rydberg atoms with principal quantum number n = 390 to one or more half-cycle electric field pulses (HCPs) with durations Tp much less than the classical electron orbital period Tn is investigated. High-n atoms subject to a series of HCPs provide a new paradigm, the "kicked atom" for the study of non-linear dynamics in Hamiltonian systems. For certain kick frequencies, dynamical stabilization is observed which corresponds to localization in phase space of the electronic state. The evolution of this localized state is probed with HCPs. A short HCP is used to examine the momentum distribution and a new technique for measuring the spatial distribution of the electron that uses a longer-duration fast-rising is demonstrated. Similar pulses also form the basis of a new approach to the manipulation of atomic ℓ-state distributions. The experimental data are compared with the results of classical trajectory Monte Carlo simulations. In all cases good agreement between theory and experiment is observed demonstrating that quantum/classical correspondence holds at high-n.

Permanent magnets are used to selectively remove the fast atoms from an atomic beam and to guide the remaining slow atoms into a trapping region. The permanent magnets establish a quadrupole field which extends along the axis of a bent vacuum nipple. A threshold velocity is set by the radius of curvature of the bent nipple and the strength of the magnets. Only those atoms which are slower than the threshold are transmitted to the trapping region. For a 30 cm radius of curvature and a Maxwellian velocity distribution at the atomic beam source, a flux of 10$\sp9$ atoms/s is expected to be delivered to the trapping region. Experimentally, a flux of only 10$\sp6$ atoms/s is observed. The flux deficit is attributed to an attenuation of slow atoms resulting from collisions within the nozzle of the recirculating oven which is used to produce the atomic beam.

This research utilizes the Electron Shelving (ES) technique to obtain a lifetime measurement of the 3P1 energy state of strontium. The 5s21 S0 → 5p 3 P1 intercombination transition is important because of its promising usefulness in optical frequency standards and high resolution spectroscopy. Unfortunately, the transition lacks a high photon scattering rate to produce a significant signal for optical studies and therefore it is advantageous to monitor the vastly stronger 1S 0 →1 P1 transition. This lifetime measurement yielded a value of tau = 23 +/- 3 mus (systematic uncertainty), which is longer than other current experimental values established in literature. Additional lineshape studies with a dependence on magnetic fields, gravitational acceleration, and laser power were performed and are discussed briefly. These lineshape studies allow an upper linewidth limit to be placed on the pumping laser causing this transition, making these secondary studies a useful method to characterize the laser.