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The Characterisation of Molecular Alkali‐Metal Azides
Author(s) -
Ogden J. Steven,
Dyke John M.,
Levason William,
Ferrante Francesco,
Gagliardi Laura
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200501101
Subject(s) - chemistry , alkali metal , isotopomers , matrix isolation , metal , infrared spectroscopy , molecular orbital , ab initio , thermal decomposition , infrared , nitrogen , atom (system on chip) , ab initio quantum chemistry methods , molecular vibration , crystallography , molecule , organic chemistry , physics , computer science , optics , embedded system
Matrix isolation infrared (IR) studies have been carried out on the vaporisation of the alkali‐metal azides MN 3 (M = Na, K, Rb and Cs). The results show that under high vacuum conditions, molecular KN 3 , RbN 3 and CsN 3 are present as stable high‐temperature vapour species, together with variable amounts of nitrogen gas and the corresponding metal atoms. The characterisation of these molecular azides is supported by ab initio molecular orbital calculations and density functional theory (DFT) calculations, and for CsN 3 in particular, by the detection of the isotopomers Cs( 14 N 15 N 14 N) and Cs( 15 N 14 N 14 N). The IR spectra are assigned to a “side‐on” ( C 2 v ) structure by comparison with the spectral features predicted both by vibrational analysis and calculation. The most intense IR features for KN 3 , RbN 3 and CsN 3 isolated in nitrogen matrices lie at 2005, 2004.4 and 2002.2 cm −1 , respectively, and correspond to the N 3 asymmetric stretch. The N 3 bending mode in CsN 3 is identified at 629 cm −1 . An additional feature routinely observed in these experiments occurred at approximately 2323 cm −1 and is assigned to molecular N 2 , perturbed by the close proximity of an alkali‐metal atom. The position of this band appeared to show very little cation dependence, but its intensity correlated with the extent of sample thermal decomposition.