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Actinic lamps in the far UV region
Low-pressure discharge lamps, hydrogen lamps, have very rich spectral lines in the 800~2000A region, while high-intensity rare gas discharge lamps also have characteristic spectral lines in the ultraviolet region. Such as: Kr (1165, 1236A) and Xe (1296, 1470A). Hot cathode low-pressure mercury lamps filled with H₂, He, Ar or N₂ can radiate in the 500~1650A region. High-intensity Schumann-ultraviolet radiation spectrum lines can be obtained by using electrodeless microwave discharge, filled with low-pressure inert gas (Xe, Kr and Ne). Its emission intensity is very high, exceeding 104 quanta/second. Moreover, it is quite monochromatic light. Therefore, it can be used in photochemical reactions.
1. Sealed rare gas resonance lamp
McNesby and Okabe described the structure and emission spectrum of Xe and Kr lamps. Figure 9-5 is a simple electrodeless discharge lamp that uses a 2450 MHz microwave generator to discharge and uses a getter to eliminate impurity spectral lines caused by trace water. The lamp is filled with about 0.7 mmHg of Xe or Kr and sealed. The lamp has a life of about 50 hours at an intensity of 10'~10'6 quantum/second.
The Ar resonance lamp emits two spectral lines: 1048A and 1067A, with an intensity ratio of about 1:2, which is related to the window thickness. The total light intensity output is on the order of 10'*~10' quantum/second. In order to eliminate the impurity spectral lines, the argon lamp must be baked at 350C for at least 12 q. Therefore, a heat-resistant Ag-AgC1 adhesive is used to seal the thin LiF window to the tube. However, within a few hours, the lamp output will drop significantly, so it must be reheated to restore performance.
Kr resonant lamps mainly produce two spectral lines, 1165A and 1236A, with an intensity ratio of 1:4, and a total output of about 10'~10' quantum/second.
Xe resonant lamps produce two main spectral lines, 1295A and 1470A, with an intensity ratio of 1:50, and a total output of about 10"~10'" quantum/second.
In addition, Ne produces 735.9A and 743.7A: He produces 584.4A spectral lines: H produces 1215.7A; D₂ produces 1215.3A spectral lines.
2. Mercury resonant lamps
The strong resonance lines emitted by low-pressure mercury lamps (<0.1mmHg) are mainly 1849A and 2537A. The lamp is filled with Hg and mmHg Ar, and is excited by non-polar microwave discharge. This lamp is particularly useful in initiating sensitization reactions.
3. Hydrogen lamp
Hydrogen lamp excited by electric discharge or microwave discharge produces many linear spectra within 1000A~1800A.
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