Instrumental Development in Time Resolved Infrared Spectroscopy with Microsecond Time Resolution

本研究是由反应中间体的物理有机化学家专家和光谱仪器的技术专家共同努力，开发一种微秒时间分辨率的时间分辨红外光谱（TRIR），用于研究有机分子光解过程中的瞬态产物。为了及时正确地评估和修改设备，通过提供瞬态物种光谱特征的基质分离光谱（MIS）和提供衰变动力学的时间分辨紫外-可见光谱（TRUV）仔细选择适合该研究的前体化合物。因此，对一系列二芳基重氮甲烷和芳基酰胺进行了辐照，用MIS记录了瞬态光产物的光谱并测定了结构，用TRUV测量了这些中间体的动力学数据。TRIR装置由Xe闪光灯、准分子和YAG激光器作为激发光源，使各种前体分子被光激发，氙红外监测光组成。监测光通过样品池，用常规红外光谱仪和探测器进行分析。然后利用计算机系统对瞬态红外光谱的衰减曲线进行了积分和分析。由于前体分子和溶剂与瞬态碳的吸收重叠，用TRIR闪光光解重氮甲烷效果不佳。然而，类似的芳基酰亚胺在正庚烷中的闪光光解提供了一种瞬态吸收，这是由于芳基亚烯扩环而产生的脱氢氮卓类化合物，并成功地测定了氮卓类化合物的寿命。

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.