Abstract
Fast time-resolved step-scan FT-IR (s<sup>2</sup>-FT-IR) has been used to study excited states and reaction intermediates in conventional and supercritical solvents. We have developed a four-port IR cell for s<sup>2</sup>-FT-IR measurements. The generation of W(CO)<sub>5</sub>(Xe), following photolysis of W(CO)<sub>6</sub> in supercritical Xe, has been used to optimize our s<sup>2</sup>-FT-IR measurements in supercritical fluids using the four-port IR cell. We have compared a number of different approaches for obtaining transient time-resolved IR (TR-IR) data. The IR diode-laser-based and s<sup>2</sup>-FT-IR approaches for TR-IR have been compared directly. The kinetic decay of the CpMo(CO)<sub>3</sub> (Cp = η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) radical in supercritical CO<sub>2</sub> has been determined using both TR-IR approaches, and we find no significant difference in signal-to-noise between these techniques for most of our TR-IR kinetic measurements. We have attempted to compare s<sup>2</sup>-FT-IR to the scanning dispersive TR-IR method by obtaining the infrared spectrum of the triplet excited state of 4-phenylbenzophenone, which has been published previously. The importance of obtaining high spectral resolution s<sup>2</sup>-FT-IR spectra for reactions in condensed phases is investigated. The IR spectrum of the CpFe(CO)<sub>2</sub> radical in <i>n</i>-heptane shows that important information regarding the structure of the radical can only be obtained by performing time-resolved s<sup>2</sup>-FT-IR experiments at high spectral resolution.
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