Teledyne 102E SO2 + hv214nm ⎯⎯Ia⎯→ SO2, SO2 * ⎯⎯→ SO2 + hv330nm, Ia = I0 1 − exp− axSO2, Equation

THEORY OF OPERATION	M102E/M501 TRS
	(Addendum to M101E Manual - P/N 04740 Rev A)

nm. The SO2 molecules absorbs some of energy from the UV light causing one of the electrons of each of the affected molecules to move to a higher energy orbital state.

SO2 + hv214nm ⎯⎯Ia⎯→ SO2 *

(Equation 9-2)

The amount of SO2 converted to excited SO2* 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 SO2 as the light travels through the sample gas.

Darkened	214nm		UV
REACTION CELL	Filter
filled with SO2		SOURCE

Figure 9-1: UV Absorption in the M102E Reaction Cell

The equation for defining the average intensity of the UV light (Ia) is:

Ia = I0 [1 − exp(− ax(SO2 ))]

(Equation 9-3)

Where:

I0 = Intensity of the excitation UV light.

a= The absorption coefficient of SO2 (a constant).

SO2 = Concentration of SO2 in the sample chamber.

x= The distance between the UV source and the SO2 molecule(s) being affected (path length).

The second stage of this reaction occurs after the SO2 reaches its excited state (SO2*). Because the system will seek the lowest available stable energy state, the SO2* molecule quickly returns to its ground state (Equation 10-3) by giving off the excess energy in the form of a photon (hν). The wavelength of this fluoresced light is also in the ultraviolet band but at a longer (lower energy) wavelength centered at 330nm.

	SO2 * ⎯⎯→ SO2 + hv330nm
	(Equation 9-4)
44	05514 Rev A1