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Theory Of Operation Teledyne API M100E Analyzer Operation Manual
220
The amount SO
2
converted to
excited SO
2
* in the sample chamber is dependent on the average intensity of the
UV light (
Ia) and not its peak intensity because the intensity of UV light is not constant in every part of the
sample chamber. Some of the photons are absorbed by the SO
2
as the light travels through the sample gas.
Darkened
REACTION CELL
filled with SO
2
214nm
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UV
SOURCE
Figure 11-1: UV Absorption
The equation for defining the average intensity of the UV light (Ia) is:
20
SOaxexp1IIa
(Equation 11-2)
Where:
I
0
= Intensity of the excitation UV light.
a = The absorption coefficient of SO
2
(a constant).
SO
2
= Concentration of SO
2
in the sample chamber.
x
= The distance between the UV source and the SO
2
molecule(s) being affected
(path length).
The second stage of this reaction occurs after the SO
2
reaches its excited state (SO
2
*). Because the system will
seek the lowest available stable energy state, the SO
2
* molecule quickly returns to its ground state (Equation 10-
3) by giving off the excess energy in the form of a photon (h). The wavelength of this fluoresced light is also in
the ultraviolet band but at a longer (lower energy) wavelength centered at 330nm.
nm33022
hvSO*SO
(Equation 11-3)
04515F DCN6048