Room temperature spectroscopic investigations of (KNO3)-N-14, (KNO3)-N-15,(KNO3-x)-N-14-O-16 O-18(x) and a 1 : 1 mixture of (KNO3)-N-14 and (KNO3)-N-15: Intermolecular coupling revealed in the vibrational spectra

The diffuse reflectance Fourier transform IR (DRIFT) and Raman spectra for microcrystalline (KNO3)-N-14, (KNO3)-N-15, (KNO3-xOx)-N-14-O-16-O-18 and a 1:1 mixture of (KNO3)-N-14 and (KNO3)-N-15 were measured at room temperatur e. A new assignment for the observed factor group split components of the a symmetric N-O stretching mode and infrared evidence for the existence of dy namically disordered NO3- ions is proposed. Attractive intermolecular dipol ar interaction among the NO3- ions along the chain is invoked to explain th e spectral features around the asymmetric stretching mode region in the Ram an spectrum of the 1:1 mixed salt of (KNO3)-N-14 and (KNO3)-N-15. Analysis of the experimental data for the oxygen-enriched salt also demonstrates the existence of intermolecular coupling in the asymmetric stretching mode reg ion. The intensities of the Raman components of the totally symmetric N-O s tretching and in-plane bending mode regions correlate almost quantitatively with the calculated distribution of the various isotopes of NO3- ions in O -18-enriched KNO3. The IR intensity of the corresponding bands, on the othe r hand, is dependent on the symmetry of the respective isotopic species. Co pyright (C) 1999 John Wiley & Sons, Ltd.