Knowledge Bank

High resolution absorption spectra of the 2.0-3.5 $\mu$ region of a basal section of calcite are reported and analyzed. The resolution was accomplished with a 7500 1.p.i. ""Merton-N.P.L."" replica grating mounted in place of the Littrow mirror of a Perkin-Elmer Model 13 Spectrometer, with a KBr prism left in place. The spectrum is of the ""double beam"" type, although it envelopes the region of the $3700cm-1$ water vapor fundamentals. The methods of accomplishing the necessary compensation are discussed. Further details of the well known splittings of degenerate vibrations of the $CO3$ ion were observed and will be discussed in terms of the relative importance of the terms $Vmm\prime$ and $Vjmsr$ in the complete expression for the vibrational potential energy function of a crystal suggested by $Hornig.1$ In this analysis, the expected differences in the spectra of the so-called ordinary and extraordinary rays is discussed in terms of the theory of the motions of molecules in condensed systems developed since such spectra were obtained. An alternate explanation of some of the observed ""splittings"" in the $2.0-3.5\mu$ region, will be presented. This analysis will be similar to that suggested previously as an explanation of observed fine structure in the spectra of crystalline iodoform and brucite. In this test of the explanation, spectra of calcite were obtained from $78\circ K$ to $873\circ K$; the observed modifications in the spectra confirm the hypothesis of ""librational interaction"".