So Ultraviolet Fluorescence; Figure 10-1. Uv Absorption In The T102 Reaction Cell - Teledyne T102 Operation Manual

THEORY OF OPERATION
10.1.2. SO
Ultraviolet Fluorescence
2

Figure 10-1. UV Absorption in the T102 Reaction Cell

I
0
a
SO
x
56
The physical principle upon which the T102's measurement method is based is the
fluorescence that occurs when sulfur dioxide (SO
by ultraviolet light with wavelengths in the range of 190 nm-230 nm. This reaction is a
two-step process.
The first stage (Equation 9-2) occurs when SO
the appropriate ultraviolet wavelength. (In the case of the Model T102, a band pass filter
between the source of the UV light and the affected gas limits the wavelength of the light to
approximately 214 nm). The SO
of the electrons of each of the affected SO
state.
+
SO hv
2
The amount of SO converted to SO
2
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 as the light travels through the sample gas.
2
The equation for defining the average intensity of the UV light (Ia) is:
[
=
Ia I 1
0
Where:
=
Intensity of the excitation UV light.
=
The absorption coefficient of SO
=
Concentration of SO
2
=
The distance between the UV source and the SO
affected (path length).
Teledyne API - T102/501 TRS, Addendum to T101 Operation Manual
molecules are struck by photons (hv) of
2
absorbs some of energy from the UV light causing one
2
molecules to move to a higher energy orbital
2
 →
Ia
SO
214 nm 2
* in the sample chamber is dependent on the
2
( ( )
− −
exp ax SO
2
(a constant).
2
in the sample chamber.
2
) is changed to an excited state (SO
2
*
Equation 10-2
]
)
Equation 10-3
molecule(s) being
2
07267B DCN6485
*)
2