Experimental Details

This chapter describes spectroscopic systems for observing the spectra of transient molecules, by placing main emphasis on the spectrometers which my group has set up and employed to observe high-resolution spectra of transient species. The high reactivity and thus the short lifetime of such molecules require that the spectroscopic methods are highly sensitive. Introduction of lasers as sources has increased the sensitivity, in particular in the IR region, where the light sources hitherto available were of low output. Improvement of detectors has also contributed much to the increase of sensitivity. In conventional optical and IR spectroscopy the resolution has been incompatible with the sensitivity, because to attain high resolution one had to reduce the slit width and thus lose the power entering the detector. This difficulty has been eliminated to a great extent also by using lasers as sources. One might think that high resolution may not be indispensable for the study of transient molecules, rather it may make the spectroscopic method cumbersome to use and may limit its applicability range. That this is not the case is indicated by noting that transient molecules exist only with many other molecules that are either reactants or products of the reaction generating them. High resolution enables us to observe spectra of transient species nearly or completely isolated from much stronger spectra of much more abundant, chemically stable molecules. Obviously, high resolution brings about very precise data on molecular constants including the fine and hyperfine coupling constants characteristic of free radicals. These data are central in understanding the molecular structure of free radicals.