IR Spectra and Vibrational Analysis of Isotopomers of KNO₃in Solid Ar

Author： Lo W-J. Shen M-y. Yu C-h. Lee Y-P.

ISSN： 0022-2852

Source： Journal of Molecular Spectroscopy, Vol.183, Iss.1, 1997-05, pp. : 119-128

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Abstract

Infrared absorption spectra ofMNO₃(M= Li, Na, and K) in solid Ar were recorded with a FTIR spectrometer. The absorption of KNO₃displayed only singlet lines, at 1460.3, 1293.5, 1031.4, 828.0, 721.4, and 709.4 cm^-1, whereas that of LiNO₃and of NaNO₃showed doublets or multiplets due to matrix site splitting. Hence, detailed vibrational analysis of the NO₃^-moiety was made for KNO₃. From spectra of KN¹⁶O_3-x¹⁸O_x(x= 0–3) and K¹⁵NO₃, five vibrational modes are unambiguously assigned and a bidentate structure of KNO₃is confirmed. The line at 721.4 cm^-1, previously assigned to aB₂mode, is reassigned to the &ngr;₃(A₁) mode. A weak line at 709.4 cm^-1, of which¹⁸O-isotopic data are lacking, is tentatively assigned to the &ngr;₈(B₂) mode. A Fermi resonance due to the &ngr;₁(A₁) and a combinational band of &ngr;₇(B₂) +&ngr;₉(B₂) was observed for K(¹⁸O¹⁸O)N¹⁶O at 1465.8 and 1451.7 cm^-1. Normal coordinate analysis was performed for the five vibrational modes of all isotopic species. The results are consistent with theoretical predictions using density functional theory (B3-LYP).