The experimental ATR bands for thengr;3nitrate ion mode, in particular as measured for trigonal alkalimetal nitrate crystals with their trigonal axes perpendicular to the ATR elementndash;sample interface, display interesting shapes which are radically different forTMandTEpolarizations. Further, there is only a marginal amount of overlap of the intense bands which appear for the two polarizations. It is shown that the band structures are in complete accord with expectations based on a damped oriented oscillator model of the nitrates combined with the complex form of Snell's law and Fresnel's reflection equations as developed for a uniaxial crystal. The theoretical development indicates that theTMband structure closely reflects both the transverse and longitudinal modal frequencies since the band peaks sharply nearngr;3lpar;trpar;and has an inflection point corresponding tongr;3lpar;lrpar;. This insight is used to deducengr;3lpar;trpar;andngr;3lpar;lrpar;from ATR data for the highhyphen;temperature trigonal forms of sodium and potassium nitrate.
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