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Actinic light source - low pressure mercury lamp
When the mercury vapor pressure is relatively low, 133,3X10-*Pa (10-*mmHg), mercury atoms are more likely to be excited to the 6*P1 energy level. When the atoms in this excited state return to the ground state, they produce resonance radiation with a wavelength of 2536.5A.
Hg (*P1) →Hg ('S.) +hv (2536.5A)
In addition, mercury atoms can also be excited to the 6'P: energy level and return to the ground state to produce a wavelength of 1849A.
Hg('P1)→Hg('S.)+hv'(1849A)
When the mercury vapor pressure is 799.8x10-spa (6x10-3mmHg), the energy of this resonance radiation accounts for the largest proportion of the input electrical energy. That is, at this time, the radiation effect of 253.7nm is the largest, about 60%, while the visible radiation is very small, accounting for only about 2% of the input electrical energy, so it is effective for photochemical reactions. Therefore, the radiation of 2537A (equivalent to 112.73 kcal/mo1) is the most used in photochemical reactions. This is also the reason why the photochemical light source is generally selected as a mercury lamp. Low-pressure mercury lamps are more in the ultraviolet region. Ultrahigh-pressure mercury lamps are less, but the absolute amount of ultraviolet rays is the largest in medium-pressure mercury lamps.
Low-pressure mercury lamps have developed into three forms today: one is the hot cathode arc discharge type, the second is the cold cathode glow discharge type, and the third is the electrodeless microwave excitation discharge type.
The hot cathode mercury gas discharge lamp has a very low operating voltage and a large current. In my country, cold cathode mercury gas discharge lamps are mainly used as ultraviolet light sources. The GD30 type 30-watt ultraviolet sterilization lamp has a lamp diameter of 7mm, an inter-electrode distance of 600mm, an operating voltage of 500V, a starting voltage of 1600V, and an operating current of 36mA. Electrodeless mercury gas discharge lamps require microwave generators, such as: 2450MH₂ oscillators, which can produce radiation spectra with very narrow resonance lines.
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