DOUBLE MODULATION-HIGH RESOLUTION INFRARED SPECTROSCOPIC TECHNIQUE - THE UPSILON-3 BAND OF THE CH3 RADICAL AND EXCITED-STATES OF CH4 IN A HOLLOW-CATHODE DISCHARGE

In this work several fines of the nu3 fundamental band of the CH3 radi cal have been detected in a refrigerated hollow cathode discharge mult ipass cell filled with CH4, by using a discharge and laser amplitude d ouble modulation technique, with a difference frequency laser spectrom eter and a double phase sensitive detection. Bands of the precursor CH 4 and Of C2H4 and C2H6 produced in the discharge have been observed to o. By Doppler broadening and absorption variations, the increase of te mperature with the establishment of the discharge has been tested. It is only approximately 15-degrees-C. Nevertheless, a very high sensitiv ity in transmittance variations with temperature is achieved for trans itions from highly excited levels of stable species. The method propos ed can be very useful for the assignment of very weak bands.