Gas phase molecular ions are of considerable interest and importance in many areas of chemistry and physics. They have been identified in many diverse areas ranging from the interstellar medium, comets, the earth's atmosphere, through to flames and plasmas. In some instances, studies of molecular ions in extra-terrestrial sources have pre-empted laboratory based experiments or calculations and vice-versa. Through an understanding of diatomic molecular ions (their geometries and inter-atomic potentials) an insight can be gained into atom-ion interactions, yielding a greater understanding of the important processes occurring in these media [1].
Laboratory-based spectroscopic studies of molecular ions are intrinsically more difficult than for the corresponding neutral molecules due to short lifetimes which result from ion-molecule reactions. Additional losses result from ions combining with electrons or diffusing to the walls of a container. It is hence difficult to form and maintain high densities of molecular ions for study within the time scales of most standard spectroscopic techniques. The use of laser-based experiments has meant the availability of high photon densities to compensate for the low ion densities, allowing spectra for a wide range of molecular ions to be recorded.
Several reviews of the spectroscopy of molecular ions exist, including Herzberg's review of early work [2], Saykally and Woods' [3] account of high resolution techniques, Moseley's paper describing Ion Photofragment spectroscopy [4] and Maier's brief review of some current techniques (with respect to electronic transitions) [5].
The fundamental aim of the studies outlined in this thesis is to probe diatomic molecular ions, using a laser photofragment spectroscopy technique to increase the knowledge of the structure and dynamics in such systems.