## THE TEMPERATURE DEPENDENCE OF THE INFRARED REFLECTION SPECTRUM OF SODIUM CHLORIDE

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Ohio State University##### Abstract:

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 $formula^{1}$ 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$^{2,3}$ a based on consideration of an harmonic terms in the potential energy function, the damping constant should show a large temperature dependence.

##### Description:

$^{1}$ M. Born and K Huang, Dynamicol Theory of Crystal Lattices (Oxford University Press, London, 1954) p. 121. $^{2}$ M. Born K. Huang, loc. Cit. p. 341 $^{3}$ A. Maradudin and R F. Willis. Bull. Amer. phys. Soc 4, 143 (1959).

Author Institution: U.S. Naval Research Laboratory

Author Institution: U.S. Naval Research Laboratory

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