Project summary/abstract Supplemental funding is requested for a new Perkin Elmer diode array UV/Vis/Near-IR spectrophotometer with multi-sampler and sample temperature control. Our laboratory has relied on HP/Agilent 8453 UV-Vis diode array spectrophotometers for at least two decades, for this project and others. Both of our old HP/Agilent 8453 UV-Vis diode array spectrophotometers have now stopped functioning, and Agilent no longer services or makes parts for these workhorse instruments. We currently have two UV/vis spectrophotometers, but these are scanning instruments that are slow to obtain a whole spectrum and they are set up with fiber optic cables to obtain optical spectra inside of glove boxes. The rapid scanning of the diode array, the temperature control, and the multi- sample capability will accelerate the current and planned research projects supported by this award. These projects use molecular and colloidal nanoparticle systems to develop understanding of fundamental chemical processes, especially proton-coupled electron transfer and oxygen atom transfer, which play important roles in biological systems.