Laser Spectroscopy of Main Group Reactive Intermediates

This proposal sets forth a program of research to study the electronic spectra of main group reactive intermediates, concentrating on free radicals containing phosphorus, arsenic and boron. Our approach will be to use a variety of laser spectroscopic techniques to study the reactive intermediates in the gas phase. These species will be generated by ela~tron impact fragmentation of stable precursor compounds. In order to simplify complex spectra and obtain as much information as possible, the reactive species will be prepared in supersonic free-jet expansions so that they can be studied at very low rotational temperatures under collision-free conditions. Laser-induced fluorescence, wavelength-resolved fluorescence, stimulated emission pumping~ fluorescence depletion, fluorescence liiètime and r~onance enhanced multiphoton ionization techniques will be used as appropriate to characterize the jet-cooled radicals. Intellectual Merit of the Project: In our proposed spectroscopic studies, we have targeted a variety of species whose electronic spectra are largely unknown. The C,P and C,As radicals were recently identified in our laboratory and require more detailed study. PCN and AsCN were tentatively detected by conventional flash photolysis studies in 1968 but this work remains unconfirmed by experiment. Similarly, the X,PO, X2PS and X,AsO (H = H, F, Cl, Br) free radicals are new species whose electronic spectra have not been studied. From a fundamental point of view, the chemistry of phosphorus and arsenic compounds is often very different from their nitrogen analogs, which strongly motivates this work. CCP and PCN are also strong candidates for interstellar molecules but need a database of terrestrial laboratory measurements prior to searches by radioastronomy. We also know very little about the boron-containing free radicals HBX (X = F, Cl, Br), BF, and BCI,, despite their likely intermediacy in a variety of industrial processes. Preliminary studiesin our labontory have established the feasibility of most of the proposed experiments, providing strong evidence that the program of research will be successful and productive. Broader Impacts of the Proposed Research: Although the research is fundamental in nature, it has a much broader impact. Our interest in arsenic, boron and phosphoEus species stems from their importance as reactive intermediates in processes used to modify the electronic characteristies of semiconducting materials. Doping with group Ill and V elements substantially changes the pmperties of intrinsic semiconductors and our research is aimed at developing sensitive spectroscopic methods for detecting, identifying, and characterizing the free radicals that can be formed in such processes. Free radicals containing phosphorus are also of current interest in astrophysics, as they are known to exist in interstellar gas clouds and circumstellar atmospheres. The spectroscopic information obtained from the work outlined in this proposal will provide necessary data for future studies of these reactive species in industrial processes and chemical reactions. The data will also be invaluable for laboratory studies of their reaction kinetics. These spectroscopic studies will establish important primary data about the molecular structures, energy levels, and electronic transitions of a series of intermediates for which little precise information is currently available. The research will also provide training for a new generation of physical chemists in a technically demanding and challenging area of science in which there is a dearth of well-qualified practitioners.