Knowledge Bank

Reflection spectra of single crystal $Cr2O3$ and $\alpha -Al2O3$ were investigated in the region $250cm-1$ to $1200cm-1$. Kramers-Kronig analyses of the spectra gave the infrared active factor group $(k\simeq 0)$ fundamentals, consistent with the $D3d6$ point group to which the crystals belong. Transmission spectra of both compounds were studied up to $2000cm-1$ and a number of absorption maxima recorded, which were assigned to combinations of $k\ne 0$ normal $modes.1$ The assignments are consistent with the polarization and temperature dependence of the spectra.