Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 178
energy of transitions from the ground state (υ = 0), to higher levels is given by equation
(6.17) [2].
∆E = E − E = ω υ − ω x υ(
υ + 1)
(6.17)
υ 0 e e e
The transition between levels υ = 0 to υ = 1 for a molecule is known as the fundamental
transition, and is seen on vibrational spectra as the fundamental frequency. Higher
transitions, which are approximate multiples of the fundamental frequency, are known as
the first overtone (υ = 0 to υ = 2), second overtone (υ = 0 to υ = 3) etc. [2].
The harmonic model predicts equally spaced overtones, when in fact this spacing
decreases slightly with increasing energy level [2]. The disassociation energy of the
molecule, e D , is not equal to E d , but shown by equation (6.18) [2].
1 1
De = Ed
− E0
= Ed
− ωe
+ ωe
xe
(6.18)
2 4
ω e is related to ke, the anharmonic force constant and is a better representation of bond
strength than k obtained from the harmonic model [2].
Selection rules
The general selection rule for infrared vibration of a molecule is that the dipole of the
molecule must change with the atomic displacement. This process can occur as the