Instrumental Development in Time Resolved Infrared Spectroscopy with Microsecond Time Resolution

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This research was undertaken to develope a time-resolved infrared spectroscopy (TRIR) with microsecond time resolution for studying transient products involved in photolysis of organic molecules by collaborate efforts of physical organic chemists expert in reactive intermediate and technical experts in spectroscope instrumentation.In order to evaluate and modify the equipment promptly and properly, precursor compounds suitable for such study were carefully chosen by using matrix-isolation spectroscopy (MIS) which provided spectroscopic features of transient species and time-resolved UV-vis spectroscopy (TRUV) which afforded decay kinetics. Thus, a series of diaryldiazomethanes and arylazides were irradiated and the reactions were monitored by MIS where spectra of the transient photoproducts were recorded and structures were deterined and by TRUV where the kinetic data of these intermediates were measured.TRIR set-up consisted of Xe flash lamp, excimer and YAG lasers as excitation light source so that a variety of precursor molecules can be photoexcited, and xenon IR monitor light. The monitor light was passed through a sample cell and analyzed by using conventional IR spectrometer and detector. Decay curves of transient IR spectra were then integrated and analyzed by computer system.Flash photolysis of the diazomethanes with TRIR was not very fruitful partly due to overlapping absorption of the precursor molecules as well as solvents with those of the transient carbene. However, similar flash photolysis of arylazides in n-heptane provided a transient absorption due to dehydroazepines obviously produced as a result of ring-expansion of the arylnitrenes and the lifetimes of the azepines were successfully determined.