AN INFRARED RAPID SCANNING SPECTROMETER AND ITS USE IN THE MEASUREMENT OF THE SPECTRA OF SHORT-LIVED MOLECULES

Abstract

This work has been supported by the United States Air Force, Office of Scientific Research, Baltimore, Maryland.Author Institution: U. S. Naval Ordnance LaboratoryA rapid scanning infrared spectrometer has been designed and constructed to search for certain fundamental bands of the free radicals $NH_{2}$, $CH_{3}$, and $CH_{2}$. The monochromator uses the same off-axis parabola design as the Perkin-Elmer Mod. 12, but the Littrow mirror has been replaced by a Littrow-Wadsworth combination in which the Littrow mirror rotates continuously. The detector is a cooled lead telluride photoconductive cell. The spectrum is presented on a double beam oscilloscope. An ""optical vernier"" system synchronizes the oscilloscope sweep and also generates a set of linear fiduciary marks, each corresponding to about 4 minutes of Littrow mirror rotation, which are presented on the second trace of the oscilloscope. The radicals are generated by flash photolysis in one meter quartz absorption cell. This spectrometer is capable of scanning the 3 mu band of ammonia in about 4 milliseconds with essentially no loss in resolution from conventional slow speed, narrow band scanning, in about 2 msecs with slight loss, and in less than one msec with somewhat greater resolution loss. The results of using this instrument to search for the 3 micron bands of $NH_{2}$, $CH_{3}$, and $CH_{2}$ will be presented