The subject of gaseous ions has received considrable attention in the last several years. An understanding of the formation processes for ions and the role ions play in various chemical processes is of fundamental importance in describing the nature of radiation phenomena, the formation of ions and electrons in the ionosphere, the production of ions in flames, and the use of ions in qualitative and quantitative analyses of materials using mass spectrometric techniques.
In our laboratory we study negative ions using autodetachment spectroscopy. The technique offers mass resolution, access to a wide variety of of ion sources, and sub-Doppler resolution. An infra-red diode laser and an F-center laser have been effectively used to study ions such as NH- and HNO-. Please review our publications list or abstracts for more details.
The high-resolution spectroscopy of positive ions is performed using Velocity Modulation technique. Conventional absorption spectroscopy in a discharge which has been proven so fruitful for neutral molecules is very difficult to apply to molecular ions. The typical densities of molecular ions in a discharge are much lower than the densities of neutral molecules. Consequently absorption signal from ions can be masked by the much stronger interfering absorption signal from neutrals. The velocity modulation spectroscopy allows high degree of suppression of neutral signal. It also produces different lineshapes for neutrals, positive and negative ions. We have used the technique to study first high-resoulution absorption spectrum of H2O+. The work is underway to study D2O+ and HDO+
A Rydberg atom has typically one electron excited to a state of high principle quantum number n. Rydberg atoms are of interest because they possess physical and chemical properties that are quite unlike those normally associated with atoms in ground states. Because the atomic radii scale as n-squared, Rydberg atoms are enormous. The excited electron is so far from the nucleus and inner electrons (core) that its motion is significantly perturbed by external electric or magnetic fields. Rydberg levels are closely spaced in energy and have very small binding energies, typically a few meV. Their weak binding energies and large size make Rydberg atoms very fragile. Thus Rydberg atoms are easily perturbed by collisions, resulting in wide range of reaction processes, many of which are unique to Rydberg atoms and have extremely large cross-sections.
As a graduate student I measured electron transfer cross-sections to a variety of neutral molecules. In certain reactions the transient molecular ion dissocitates after electron transfer has taken place. The translational energies of the ions were measured. Such studies also helped determine the lifetimes of these transient complexes. The abstracts and the publication list provide more details.