Instrumental Development in Time Resolved Infrared Spectroscopy with Microsecond Time Resolution

本研究通过有机反应中间体物理化学家和光谱仪器技术专家的共同努力，开发了一种用于研究有机分子光解瞬态产物的时间分辨红外光谱仪，该仪器具有微秒级的时间分辨率，为了及时、合理地对仪器进行评价和改进，通过使用提供瞬态物质的光谱特征的基质隔离光谱（MIS）和提供衰变动力学的时间分辨紫外-可见光谱（TRUV），仔细选择适合于这种研究的前体化合物。因此，一系列的二芳基重氮甲烷和芳基叠氮化合物的辐照和反应的监测MIS的瞬态光产物的光谱记录和结构确定和TRUV的这些中间体的动力学数据，TRIR装置包括双金属闪光灯，准分子和YAG激光器作为激发光源，以便各种前体分子可以被光激发，和氙IR监测光。监测光通过样品池，并使用常规的红外光谱仪和检测器进行分析。对瞬态红外光谱的衰减曲线进行了计算机积分和分析，发现TRIR对重氮甲烷的闪光光解反应效果不佳，部分原因是前体分子和溶剂的吸收与瞬态卡宾的吸收重叠。然而，类似的闪光光解的芳基叠氮化物在正庚烷中提供了一个瞬态吸收，由于脱氢氮杂卓显然产生的结果的芳基氮杂环化合物的扩环和氮杂卓的寿命被成功地确定。

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.