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Colour centres in alkali metal azides

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Title: Colour centres in alkali metal azides
Author: Pringle, John Peter Scott
Degree: Master of Science - MSc
Program: Chemistry
Copyright Date: 1958
Subject Keywords Spectrum analysis;X-rays -- Diffraction
Issue Date: 2012-01-18
Publisher University of British Columbia
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]
Abstract: Previous work by Heal had shown that X-irradiated sodium azide crystals dissolved in water produced small amounts of nitrogen gas, hydroxyl ion and ammonia, thereby indicating that some decomposition had occurred. Heal also observed colours in the material, similar to those of the X-irradiated alkali halides for which a whole series of colour centres responsible have been postulated. It was therefore decided to investigate the colour centres of the alkali azides, partly to extend the colour centre research, and partly to illuminate the X-ray decomposition processes. Crystalline plates of NaN₃, KN₃, RbN₃ and CsN₃ were irradiated at liquid nitrogen and room temperature, using a Machlett AEG-50 tungsten target X-ray tube, operated at 50 KVP. The absorption spectra of the irradiated samples were measured at liquid nitrogen temperature with a Cary model 14 recording spectrophotometer. The low temperature spectra consisted of three bands. The A band, peaking at 612, 568, 578 and 592 mu for NaN₃, KN₃, RbN₃ and CsN₃, respectively, is ascribed to F centres. The anomalous sodium azide band is related to its trigonal crystal structure, differing from the body centred tetragonal of the other azides. The B band, peaking at 361, 374 and 390 mu for KN₃, RbN₃ and CsN₃ respectively, was strong and triple, there being shoulders about 30 mu on each side of the main peak. For NaN₃ it was weak, single and peaked near 330 mu. Tentatively, it is ascribed to the centre. The C band, peaking about 740, 790, 820 and 850 mu for NaN₃, KN₃, RbN₃ and CsN₃ is weak and single. It may be due to F1 centres. The room temperature spectra were strikingly different from each other, except for RbN₃ and CsN₃. For NaN₃ five bands were observed at 342, 560, 630 , 730 and 860 mu; the latter four were weak and may be an electronic vibrational spectrum. The strong 342 mu band is ascribed to the presence of sodium metal in some non-colloidal form; a correlation between the band and the ionisation potential of the metal is noted. In KN₃ three bands at 760 (strong), 590 (strong shoulder) and 340 mu (weak) were obtained. The first two are ascribed to small F centre aggregates of the M,R type though no definite assignations are made. RbN₃ and CsN₃ spectra both consist of a broad peak showing fine structure, the highest peaks occurring at 330 mu and 375 mu respectively. It is considered uncertain that all the absorption is due to the impurity held responsible for the fine structure.
Affiliation: Science, Faculty of
URI: http://hdl.handle.net/2429/40162
Scholarly Level: Graduate

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