Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 176
Absorption results from the excitation of the molecule from υ = 0 to υ = 1, and so on, by
the incident radiation. This gives ∆E = hω, and k can be obtained by rearranging equation
(6.14) [2].
The anharmonic oscillator
The parabolic potential well shown by equation (6.13) and fig. (6.3) is not an accurate
model of the variation in force experienced by a diatomic molecule. Equation (6.13)
represents a symmetric potential well, whereas in reality it would be asymmetric [2]. As
the nuclei come together, they repel each other and the potential energy will rise
exponentially, similar to the harmonic oscillator. However, as the nuclei are pulled apart,
the potential energy will level off as dissociation occurs, resulting in an asymmetric
potential well. An empirical equation known as the Morse potential, can be used to model
this behaviour. This is shown by equation (6.15) [2].
E
−κq
2
p = Ed
( 1−
e )
(6.15)
where Ed = depth of the potential well, and κ = curvature of bottom of the potential well.
This is graphically illustrated in fig. (6.4).