Computer Science
Scientific paper
May 1960
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1960natur.186..712b&link_type=abstract
Nature, Volume 186, Issue 4726, pp. 712-713 (1960).
Computer Science
3
Scientific paper
MOST of the methods in current use for producing radicals from crystalline solids for study by electron spin resonance involve the use of high-energy radiation and therefore require comparatively expensive and elaborate equipment. Papazian1,2 showed that several substances, including hydrazoic acid and methyl iodide, condensed from the vapours at liquid-nitrogen temperature developed colour when sparked with a Tesla-coil; this was attributed to free-radical formation. Using the electron spin resonance technique we have found that radical concentrations as high as 1018/gm. (approximately 10-3 mole 1.-1) can be obtained by applying the discharge from an ordinary vacuum leak-tester to finely ground crystals of many organic substances contained in partially evacuated electron spin resonance specimen tubes. For low-melting solids, for example some vinyl monomers, the following procedure is sometimes convenient. The degassed liquid is frozen in a thin layer on the walls of the evacuated tube, which is then cooled to -195° C. and vibrated vigorously. The crystals are thus detached from the walls and deposited in a fine powder at the bottom of the tube. A suitable gas at a pressure of about 0.1 mm. mercury is admitted and the probe of the Tesla-coil applied in the neighbourhood of the crystals, the tube being maintained at a low temperature and preferably vibrating. With high-melting solids it suffices to grind the crystals finely in a mortar before introduction into the specimen tube. Nitrogen, hydrogen, argon and oxygen have been used, in order of decreasing effectiveness. The presence of a gas is desirable but not absolutely essential. The spectrum obtained is independent of the nature of the gas. Radical concentrations of the order of 10-4 mole 1.-1 are often produced in a few seconds by this technique. Substances examined include glycine, diketopiperazine, acrylamide, potassium and lithium methacrylates, acrylic, methacrylic, n-butyric and itaconic acids, acrylonitrile and polyacrylonitrile, all of which gave strong radical spectra. Surprisingly, a negative result was obtained with azo-bis-isobutyronitrile. The radicals from these compounds show widely differing thermal stabilities and reactivities towards oxygen.
Bamford C. H.
Jenkins Alastair D.
Ward John C.
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