Ultraviolet hydrogenation difference spectra

Continuous sources The sources of choice for measurements in the ultraviolet spectral region are hydrogen or deuterium lamps [1]. When the gas pressure is 30 to 60 X10 Pa they yield a continuous emission spectrum. The maxima of their radiation emission occur at different wavelengths (Hi A = 280 nm Di 2 = 220 nm). This means that the deuterium lamp is superior for measurements in the lower UV region (Fig. 15). 

The electronic spectrum of a compound arises from its 7r-electron system which, to a first approximation, is unaffected by substitution of an alkyl group for a hydrogen atom. Thus, comparison of the ultraviolet spectrum of a potentially tautomeric compound with the spectra of both alkylated forms often indicates which tautomer predominates. For example, Fig. 1 shows that 4-mercaptopyridine exists predominantly as pyrid-4-thione. In favorable cases, i.e., when the spectra of the two alkylated forms are very different and/or there are appreciable amounts of both forms present at equilibrium, the tautomeric constant can be evaluated. By using this method, it was shown, for example, that 6-hydroxyquinoline exists essentially as such in ethanol but that it is in equilibrium with about 1% of the zwitterion form in aqueous solution (Fig. 2). 

Experimental Procedure. As source of ultraviolet light the Author used sparks between zinc electrodes, the hydrogen lamp (which gives a continuous spectrum), or mercury lamps of differing model and power, fed by alternating or by direct current all the mercury lamps emit an arc spectrum. The spectra from these sources were determined by a spectrograph with quartz optics or a diffraction spectrograph with a fluorite window. ... 

Chemiluminescence is also shown with a few simple mineral compounds. Otto (21) expressed the opinion that, if ozone causes a luminescence in the presence of water, it acts upon impurities therein. Hydrogen sulfide gives rise to an ultraviolet chemiluminescence with ozone (Zabiezynski and Orlowski, 33). Several oxygen compounds of nitrogen, especially nitric oxide, show, under the action of ozone, a spectrum different from that of active nitrogen [Morren (20), Sarrasin (23), Strutt (26), Knauss and Murrey (17) ]. Solid phosphorus trixode becomes luminescent [Thorpe and Tutton (29)]] and so do carbon monoxide, carbonyl sulfide, and carbonyl chloride at 200 C. The first of these furnishes a band spectrum of 4000 to 5000 A. which corresponds to a bimolecular process [Trautz and Seidel (31) and Trautz and Haller (30)]. Siloxane too shows oxyluminescence [Kautsky and Zocher (16)] under the influence of ozone. 

---