The Heat Of Dissociation Of Oxygen As Estimated From Photochemical Ozonization

614 CHEMISTRY: 0. R. WULF PROC. N. A. S. THE HEAT OF DISSOCIATION OF OXYGEN AS ESTIMATED FROM PHOTOCHEMICAL OZONIZA TION By OLIVnR R. WULT * CHZMICAI LABORATORY, UNIVZRSITY OF CALIFORNIA Communicated June 23, 1928 The heat of dissociation of oxygen has been estimated by Warburg1 and by Born and Gerlach,2 using, in both cases, the data of Warburg3 on the photochemical formation of ozone. The assumptions made, however, were different, and quite different results were obtained, 138,000 calories in the former case as compared with 162,000 calories in the latter. The author believes that the estimation made by Born and Gerlach rests upon a mistaken assumption. The agreement of their result with the more recent determinations made by Hogness and Lunn4 from positive-ray studies, and by Birge and Sponer5 from spectroscopic data, appears to be fortuitous. The author further believes, from a recent study of the existing data on the absorption of light by gaseous and liquid oxygen,6 that the estimation made by Warburg' pertains probably to the molecule 04 rather than 02. The purpose of this paper is to give briefly the evidence which supports these statements. During his classical researches, which constitute the foundation of modern photochemistry, Warburg studied the formation of ozone from oxygen at wave-lengths 2530 A and 2070 A.3 At the latter he found conditions which nearly satisfied the photochemical equivalence equation, while at the former this was not the case. Wave-length 2530 A was the longest used, because, even at the high pressures worked with, oxygen does not absorb appreciably much further to the red. In the estimation made by Born and Gerlach, one finds the important basis of the calculation to be contained in the statement that the longest wave-length which forms ozone is 2530 A, making reference to the work of Warburg.3 But there does not seem to be su