Teledyne T101, Operation Manual, Page: 251 / 375

Teledyne ML - T101 Operation Manual Principles Of Operation
247
Figure 10-1. UV Absorption
The equation for defining the average intensity of the UV light ( Ia ) is:
( ) ( )
[ ]
2 0
SO ax exp 1 I Ia
− − =
Where: (Equation 10-2)
I
0
=
Intensity of the excitation UV light.
a
=
the absorption coefficient of SO
2
.
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
ν
). The wavelength of this fluoresced light is also in the ultraviolet
band but at a longer (lower energy) wavelength centered at 330nm.
nm 330 2 2
hv SO * SO
+   → 
(Equation 10-3)
The amount of detectable UV ( F ) given off by the decay of the SO
2
* is affected by the rate
at which this reaction occurs ( k ).