Influence of swelling stresses on the shift of Raman vibration peaks

An interesting effect in silica glass is the shift of IR- and Raman-peaks
under externally applied stresses. A first interpretation of the influence of
stress on the IR frequency was made possible by its influence on the bond
angles, as had been shown very early by Galeener [1]. In this interpretation,
the stress effect is assumed as a consequence of a change of the bond
angles due to the stresses.
In [2] we could show that the angle stretching is not the only effect that
influences the position of the frequency of IR lines. For our computations
we used the Lennard-Jones potential and could show that a tensile stress
must result in a decrease of the frequency.
In the present report, we will show in which way also the water concentra-
tion in the surface region can affect the measurements via volume swelling
due to the hydroxyl generation by the silica/water reaction.