Methods for the chemical characterization of particles or liquid droplets in the size range 1 um to 100 um with masses in the range 1 pg to 1 ug (10-12 g to 10-6 g) will be developed based on the researcher's picobalance facility (also called the electrodynamic balance or quadrupole levitator). The picobalance uses superposed ac and dc electrical fields to suspend stably a charged microparticle in a laser beam or other source of electromagnetic radiation. The forces holding the particle stationary are large enough to permit a particle to be maintained in the flow of a reactive gas, and as a result the balance chamber can be used as a chemical reactor. Spectroscopic methods will be developed and applied to study chemical reactions involving microparticles. The techniques to be explored are Raman spectroscopy, fluorescence spectroscopy and "optical resonance spectroscopy." A dual monochromator and associated optical equipment will be added to an existing picobalance facility to upgrade it to measure Raman spectra and fluorescence spectra. Spectroscopic techniques will then be used to characterize multicomponent droplets and to study photochemical reactions in single droplets and rates of gas/liquid-droplet chemical reactions. Reactions of particular interest include photopolymerization reactions within a droplet and reactions which can occur in the atmosphere.
