Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

3 APPARATUS 41At these low pressures pure 1849 and 2537A resonance lines are obtained. Threedesigns are shown in Fig. 2811s-117 . They are constructed from conventional orsuprasil quartz and have iron electrodes. The latter are welded to nickel followedby tungsten, which is sealed to the silica with lead or with molybdenum ribbon.Water cooling keeps the pressure low and hence prevents line reversal. If the temperatureof the circulating water is thermostatted, the main light-emitting tube maybe included in the furnace for the RV, when the output intensity is practicallyindependent of temperature up to 600” C. Suprasil or sapphire windows allow maximumtransmission of the 1849A line’ 16. The lamps may be operated in three ways:with a heated cathode at a low voltage; with a cold cathode at much higher startingvoltages; with an electrodeless discharge excited by microwave frequencies.The heated cathode has the longest life whereas the electrodeless type provides thenarrowest “lines”. Table 5 gives the characteristics of several commercial low-atm N2Hg 2537 lineReferences pp. 104-111Fig. 29. Pressure broadening of the 2537A “line”. From ref. 9.