Knowledge Bank

The infrared reflection spectrum of sodium chloride has been measured as a function of temperature from $300\circ K$ to $900\circ K$, The maximum reflectivity decreases with temperature going from 90% at $300\circ K$ to less than 50% at $900\circ K$. TO a first approximation the shape of the reflection, spectrum may be described using the dispersion $formula1$ for the complex dielectric constant \begin{equation} \epsilon(\omega)=\epsilon_x;+;\frac {\epsilon_0-\epsilon_{\infty}}{1-{\left(\frac{\omega}{\omega_0}\right)}^2;-;i\left(\frac{\omega}{\omega_0}\right)_{\omega_0}^{\gamma}}\end {equation} By fitting this dispersion formula to the observed data, it was possible lo estimate the damping factor, $\gamma /\omega o$. It was found that the damping constant varies approximately as the square of the temperature. According to various theoretical treatments$\mathrm{<mrow\; data-mjx-texclass="ORD">2,3</mrow>}$ a based on consideration of an harmonic terms in the potential energy function, the damping constant should show a large temperature dependence.