Photosensitized Decompositions by Excited Mercury Atoms

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CHEMISTR Y: TA YLOR AND BA TES -

PROC. N. A. S.

The writers wish to express their indebtedness to the Cleveland Fund of the American Association for the Advancement of Science for a grant of $500.00, which has been used in meeting the expenses of this work. They wish to thank C. N. Shah, who is working on the law of force adjacent to an atom nucleus, for much assistance in connection with this work. 1 Harkins and Ryan, J. Amer. Chem. Soc., 45, 2095 (1923). Rutherford, Phil. Mag., 37, 538 (1919). 3Blackett, Proc. Roy. Soc., 107, 349 (1925). 4 Petterson and Kirsch, Atomzertrammerung (1926), p. 138. 6 Harkins and Wilson, these PROCXnDINGS, 1, 276 (1915); J. Amer. Chem. Soc., 37, 1367 (1915).; Phil. Mag., 30, 723 (1915); and later papers. 2

PHOTOSENSITIZED DECOMPOSITIONS B YEXCITED MERCURY A TOMS By HUGH STOTT TAYLOR AND JOHN REGINALD BAThS LABORATORY OF PHYSICL CE1NaSTRY, PtCNCaTON UNIVERSITY Communicated November 13, 1926

A considerable photochemical literaturel on the subject of hydrogen atoms produced by collisions between excited mercury atoms and molecular hydrogen has served to indicate the potentialities of excited atoms for the purposes of photosensitization. The subject may be expanded in two directions, either by the use of other excited atoms or by the study of other collisions with the excited mercury. Of this latter type is the investigation by Dickinson and Sherrill,2 arising out of their studies of the interaction of hydrogen and oxygen in presence of mercury. They have shown that the production of ozone may be secured by the action of excited mercury and oxygen even though the excitation is only that in the region X = 2536.7 A and, therefore, presumably inadequate for the dissociation of oxygen. They suggest, therefore, that the ozone must arise by collisions between excited oxygen molecules and normal molecules. From our earlier work on the interaction of hydrogen and ethylene3 we have been led to investigate the efficiency of the excited mercury atom in a wide variety of photo-decompositions and have been able to show how efficient an agent it is for such photosensitizations. It has been possible to show that water, ammonia, ethylene, methyl and ethyl alcohols, hexane, benzene, acetone, formic acid and ethyl amine are all made sensitive to decomposition by light of wave-length 2536.7 A if the vapor exposed to the resonance radiation contains a sufficient concentration of mercury vapor. The decompositions thereby secured are, in several of the cases, many hundred-fold those secured by exposure in quartz apparatus to the whole ultra-violet spectrum of the cooled mercury arc and, in one case, the increased rate of decomposition is one-thousand fold.

Voi,. 12, 1926

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CHEMISTR Y.- TA YLOR A ND BA TES

The experimental arrangement is simple, as may be seen from the accompanying diagram. The material under study evaporates, at a known low vapor pressure from the reservoir A, is saturated with mercury at a given temperature in the saturator B, and then flows rapidly through the quartz vessel C, round which a cooled mercury arc of the type previously described by one of us' is operated. The products of reaction are then passed through two liquid air traps in which the condensible constituents are removed and the non-condensible gases (in the cases chosen for study, mainly hydrogen, nitrogen, oxygen, carbon monoxide or methane) were collected in a McLeod gauge. The rate of reaction could be measured by the rate of increase in pressure in the gauge. The gases could be analyzed in the gauge system with the aid of a platinum spiral which could be made incandescent, a copper oxide tube which could be electrically heated and a side tube which could be cooled in solid carbon dioxide or liquid air. To ascertain whether any photosensitized decomposition occurred, the

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