Infrared spectroscopy matrix isolated compounds

The infrared (IR) absorption spectra of a number of azauracils, such as 5-oxo-l,2,4-triazin-3-thione, 3-oxo-l,2,4-triazin-5-thione, and l,2,4-triazin-3,5-dithione, isolated in low-temperature nitrogen matrices have been reported. These compounds exist in low-temperature matrices exclusively in the oxothione and dithione tautomeric forms. Assignments of the observed IR bands were made on the basis of comparison of the experimental spectra with those obtained by ab initio SCF/6-311G calculations <1996SAA645>. Additionally, IR spectroscopy has been used to study the photoisomerization reaction of 6-methyl-5-oxo-l,2,4-triazin-3-thione <2005PCA7700>. The IR spectra revealed that before UV irradiation the matrix-isolated compound adopts exclusively the oxo-thione tautomeric form. 

Work has also been conducted that involved the investigation, via infrared spectroscopy, of matrix-isolated, plutonium oxides (40), with the appropriate precautions being taken because of the toxicity of plutonium and its compounds. A sputtering technique was used to vaporize the metal. The IR spectra of PuO and PUO2 in both Ar and Kr matrices were identified, with the observed frequencies for the latter (794.25 and 786.80 cm", respectively) assigned to the stretchingmode of Pu 02. Normal-coordinate analysis of the PUO2 isotopomers, Pu 02, Pu 02, and Pu 0 0 in Ar showed that the molecule is linear. The PuO molecule was observed in multiple sites in Ar matrices, but not in Kr, with Pu 0 at 822.28 cm" in the most stable, Ar site, and at 817.27 cm" in Kr. No evidence for PuOa was observed. 

The basic methods of the identification and study of matrix-isolated intermediates are infrared (IR), ultraviolet-visible (UV-vis), Raman and electron spin resonance (esr) spectroscopy. The most widely used is IR spectroscopy, which has some significant advantages. One of them is its high information content, and the other lies in the absence of overlapping bands in matrix IR spectra because the peaks are very narrow (about 1 cm ), due to the low temperature and the absence of rotation and interaction between molecules in the matrix. This fact allows the identification of practically all the compounds present, even in multicomponent reaetion mixtures, and the determination of vibrational frequencies of molecules with high accuracy (up to 0.01 cm when Fourier transform infrared spectrometers are used). 

Gas Chromatography—Matrix Isolation Infrared Spectroscopy—Mass Spectrometry for Analysis of Thermally Generated Aroma Compounds... 

The photolysis of HF in a solid Ar matrix gives Ar fluo-rohydride (HArF), which has been identified by infrared spectroscopy. Theoretical calculations indicate that HArF is intrinsically stable, owing to significant ionic and covalent contributions to its bonding, thus confirming computational predictions that Ar should form a stable hydride species with properties similar to those of the analogous matrix-isolated Xe and Kr compounds. 

Figure 1 MI/FT-IR spectra (fingerprint region) of (A) menthol, (B) neomenthol, (C) isomenthol and (D) neoisomenthol, 25 ng each. Reproduced with permission of the Society for Applied Spectroscopy from Coleman III WM and Gordon BM (1989) Examinations of the matrix isolation infrared spectra of organic compounds Part XIII. Applied Spectroscopy4Z 303.

Dunkin, I. R. and Thomson, P. C. R, Infrared evidence for tricycHc azirines and didehydrobenza-zepines in the matrix photolysis of azidonaphthalenes,/. Chem. Soc., Chem. Commun., 499,1980. Tomioka, H., Matsushita, X, Murata, S., and Koseki, S., Photochemistry of phenyl azides bearing 2-hydroxy and 2-amino groups studied by matrix-isolation spectroscopy generation and characterization of reactive o-quinoid compounds, Liebigs Ann., 1971,1996. 

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