ULTRAVIOLET-VISIBLE ABSORPTION SPECTRUM OF BROMINE
quinones, they made no attempt to prove that the faint absorption bands which they observed were not due to some reaction products. Acknowledgment. The support of the U. S. Public
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Health Service (Grant No. GM-10499) is most gratefully acknowledged. The assistance of Mr. Jess Long in some of the temperature-dependence studies is also acknowledged with thanks,
The Ultraviolet-Visible Absorption Spectrum of Bromine between Room Temperature and 440"
by A. A. Passchier, J. D. Christian, and N. W. Gregory Department of Chembtry, Universay of Washington, Seattle, Washington 98106 (Received September 19, 1966)
The absorption spectrum of Brt(g) at wavelengths between 200 and 750 mp and at temperatures between 25 and 440' has been measured. Molar absorptivities suitable for quantitative use are reported. The temperature dependence is compared with that predicted by a Sulzer and Wieland equation. A marked temperature and concentration dependence in the ultraviolet region and evidence for Br4 are discussed.
We have found it convenient and sometimes necessary in the study of certain equilibrium systems to determine the concentration of bromine vapor from its absorption of light in the visible region of the spectrum. The bromine spectrum has been studied previously by a number of investigators.'" Although results are in general qualitative agreement, no two independent studies give values of the molar absorptivity at various wavelengths with sufficient consistency for quantitative use. Only Ribaud' and Acton, Aickin, and Bayliss2 report experimental results for the temperature dependence in the visible region. Sulzer and Wielandg have developed a semiempirical theory for the temperature dependence of a continuous absorption spectrum for diatomic molecules. They conclude that the shape of a given absorption peak is essentially determined by three characteristic parameters which may be evaluated from the observed spectrum a t any one temperature. They test their equation with results for chlorine, bromine, and iodine, using the data of Acton, Aickin, and Bayliss for bromine. Recently, Seery and Britton' have reported
a study of the bromine spectrum at 25" and their results differ substantially from those of Acton, Aickin, and Bayliss. Seery and Britton have used their data to find new parameters for the Sulzer-Wieland equation but did not experimentally verify the molar absorptivities which it predicts for higher temperatures. Hence for quantitative use we have felt it essential to make an additional experimental study of the (1) G . Ribaud, Ann. Phys., 12, 107 (1909). (2) A. P. Acton, R. G. Aickin, and N. S. Bayliss, J . Chem. Phys., 4, 474 (1936). (3) L. T. M. Gray and D. W. G. Style, Proc. Roy. SOC.(London), A126, 603 (1929). (4) R. G. Aickin and N. S. Bayliss, Trans. Faraday Soc., 34, 1371 (1938). (5) D. F. Evans, J . Chem. Phys., 23, 1426 (1955). (6) G . Burns and R. G . W. Norrish, Proc. Roy. SOC.(London), A271, 289 (1963). (7) D. J. Seery and D. Britton, J . Phys. Chem., 68, 2263 (1964). (8) E. A. Ogryzlo and B. C. Sanctuary, J . Phys. Chem., 69, 4423 (1965). (9) P. Sulzer and K. Wieland, Helv. Phys. Acta, 25, 653 (1952).
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March 1967
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bromine spectrum as a function of temperature. Molar absorptivities have been determined from 300 to 750 mp a t various temperatures in the interval between room temperature and 440". The results are compared with those of previous workers and the Sulzer and Wieland treatment. A large temperature and concentration dependence observed between 200 and 300 mp has been studied in some detail and evidence for BrI is discussed. Ogryzlo and Sanctuary* have also recently published a communication on this aspect of the spectrum.
Experimental Section The spectra were obtained with a Beckman DU spectrophotometer equipped with a specially constructed cell compartment which could be heated uniformly to any desired temperature up to 500°.10 The instrument was calibrated periodically. Seven independent s:tmples of bromine were studied. Three were taken from Baker's Analyzed reagent grade (specified :is
