Radiation hypothesis

Second, the radiation hypothesis, pursued from the early 1900s through the 1920s by physicists and physical chemists, proposed a radiation- and energy-based mechanism for activation of intermediate steps in the chemical reaction mechanism, molecule by molecule. But, in the short run, this theory proved wrong. Nonetheless, the radiation hypothesis is interesting for our study because it demonstrates the development of an abstract mathematical and phys-... 

Work continued on the radiation hypothesis during the war, for example, in Perrin s laboratory by his student Nilratan R. Dhar and in the Muspratt laboratory at Liverpool, where William McCullagh Lewis succeeded Frederick George Donnan as director.78 Following the war, Perrin found it easy to interest... 

Nil Ratan Dhar, Coefficient de temperature de reactions catalytiques (Paris These d Universite, 1916) "Catalysis, Pt. IV, Temperature Coefficients of Catalysed Reactions," JCS.Trans. Ill (1917) 707762 and The Chemical Action of Light (London Blackie and Son, 1931). And Alfred Lamble and William C. McCullagh Lewis, "Studies in Catalysis, Pt. I, Hydrolysis of Methyl Acetate, with a Theory of Homogeneous Catalysis," JCS.Trans. 105 (1914) 23302342 and W. C. McCullagh Lewis, "Studies in Catalysis, Pt. VII, Heat of Reaction, Equilibrium Constant, and Allied Quantities, from the Point of View of the Radiation Hypothesis," JCS.Trans. Ill (1917) 457469. 

Letter from Perrin to Einstein, 28 August 1919 Einstein to Perrin, 5 November 1919, Einstein Collection, Institute for Advanced Study, Princeton (now housed in Jerusalem), cited originally in Nye, Molecular Reality, n. 93, 177. See F. A. Lindemann, "Note on the Significance of the Chemical Constant and Its Relation to the Behaviour of Gases at Low Temperatures," Phil.Mag. 39 (1920) 2125, cited in M. Christine King and Keith T. Laidler, "Chemical Kinetics and the Radiation Hypothesis," Archive for History of Exact Sciences 30 (1984) ... 

Lewis wrote to Paul Ehrenfest that he thought he had "hit upon something pretty fundamental." But Lewis had difficulty publishing his paper, "On the Theory of Reaction Rate," which the editor and referees of the Journal of the American Chemical Society worried was too speculative and insufficiently oriented toward experimental verification.96 Lewis ended by rejecting the radiation hypothesis, even issuing a press release to announce that a decision now had been made between the two rival theories of violent collision and radiation absorption in favor of the former. 97... 

Perrin s theory was flawed both in his failure to clearly express the radiation hypothesis in quantum terms and in his concrete examples of monomolecular reactions. Thomas Martin Lowry, recently appointed to a new chair of physical chemistry at Cambridge University, argued that Perrin s choices of chemical examples were unfortunate. 

Perhaps Perrin s continuing commitment is explained by the fact that his radiation hypothesis was an update of Marie and Pierre Curie s original explanation of radioactivity, that the apparently spontaneous emission of radiations and charged particles from molecules is activated by immanent radiations. The Curies supposed that radiations in the atmosphere or in the ether disturb the stability of the naturally radioactive elements. This hypothesis, like the radiation hypothesis of chemical activation, eventually succumbed to an explanation using electron configurations, adumbrated by the new quantum interpretation of matter and energy. 

A good deal of this work had no impact in the development of models of molecular structure and the elucidation of reaction mechanisms one reason was Perrin s own coolness to quantum wave mechanics. 108 Another, according to Oxford s Harold Thompson, who studied with Nernst and Fritz Haber, was that researchers like Lecomte "did not know enough chemistry he was a physicist." 109 Perrin, too, approached physical chemistry as a physicist, not as a chemist. He had little real interest or knowledge of organic chemistry. But what made his radiation hypothesis attractive to many chemists was his concern with transition states and the search for a scheme of pathways defining chemical kinetics. 

The effort to introduce advanced mathematics and fundamental theory into chemistry posed disciplinary difficulties for those developing quantum chemistry in the 1930s, as it did for those working on chemical kinetics and the radiation hypothesis in the 1920s (see chap. 5). Pauling, like Lewis, had dif-... 

We have seen, for example, that members of Lespieau s school of theoretical chemistry narrated a history of battle within the field of French chemistry against the institutionally powerful intellectual disciples of Deville, Berthelot and Jungfleisch, on the one hand, and against the conceptually powerful, if institutionally weak, school of Duhem, on the other hand. They situated themselves adjacent and sometimes interior to the scientific circle of Perrin, with its focus on kinetics and the radiation hypothesis, and in opposition to the... 

Chemical Kinetics and the Radiation Hypothesis." Archives for History of Exact Sciences 30 (1984) 4586. 

Lewis, William C. McCullagh. "Studies in Catalysis. Pt. VII. Heat of Reaction, Equilibrium Constant, and Allied Quantities, from the Point of View of the Radiation Hypothesis." JCS 111 (1917) 457469. 

The only apparently viable alternative mechanism to explain the observed unimolecular behavior is one that was originally proposed in 1919 by Perrin and became known as the radiation hypothesis. In the absence of any significant body of kinetic data, Perrin proposed that reactant molecules obtain the energy required... 

We seem, therefore, to have proved conclusively that, at least in this one reaction, radiation cannot alone be responsible for the process of activation. This experiment, together with the recent observations of Hinshelwood and Thompson, Hinshelwood, Ramsperger and Rice and Ramsperger, which show that typical unimolecular reactions do suffer a diminution in specific reaction rate with decreasing pressure and thus render invalid the powerful argument of Perrin, appears to remove all support from the radiation hypothesis. 

The proposal, elaboration, and eventual demise in the late 1920s (after considerable controversy) of the Radiation Hypothesis , which was introduced in the first decade of the 20th century to account for chemical reactions that were indirectly caused by radiation, has been discussed.129 There is a book on the history of radical chemistry130 and also a book co-authored by one of the participants about the development of free radical chemistry during the half century from about the end of World War II.131 The Dutch School of Catalysis,132 R Sabatier s (1854-1941) role in the discovery of catalysis,133 and the establishment and development of the Ipatieff Laboratory at Northwestern University134 have also been presented. 

The radiation hypothesis in 1918, wrong though it was, ushered in a period of stimulating theoretical approaches which have done... 

The most natural source of energy for the activation of molecules is molecular collision, but since the rate is independent of the number of collisions it would appear at first sight that the simple collision mechanism can not be responsible for the activation. Three hypotheses have been proposed to account for the activation process the radiation hypothesis, the elaborated collision hypothesis, and the hypothesis of chain reactions. 

At the outset it must be emphasized that the radiation hypothesis has been disqualified. However, dead hypotheses have a way of coming to life once in a while, and furthermore, one can often learn as much from apparent mistakes as from apparent successes. 

The radiation hypothesis was proposed in an indefinite way by Perrin as early as 1913. Simultaneously, about 1918, and 1919, Perrin in France, and W. C. Me, Lewis in England, and Trautz in Germany proposed the hypotheses which have been grouped together as the radiation hypothesis. Perrin undoubtedly had... 

For four or five years this hypothesis was received with considerable enthusiasm, and it was hoped that a relatioriL-between chemical kinetics, black body radiation laws and absorption spectra would permit a prediction of reaction rates. However, the simple radiation hypothesis was disqualified for several reasons, as follows ... 

These several experiments have been sufficient to disqualify the radiation hypothesis, but objections to this disqualification can be raised. 

In dismissing the radiation hypothesis it is interesting to consider one hypothetical experiment. ... 

We have seen that the radiation hypothesis is not supported by experiment and that it can not be used to explain the fact that unimolecular reaction rates are uninfluenced by collisions. When investigators found this avenue of explanation closed they resumed consideration of the collision hypothesis. As early as 1922 Lindemann suggested that since a time interval exists between activation, of a molecule and its dissociation the apparent connection between the two phenomena would ordinarily be lost. This view was received with increasing favor as the radiation hypothesis became more and more discredited. Rodebush7 in 1923 howed that the known facts could be explained on the basis of collisions... 

We have seen that neither the requirements for activation energy nor the fact that the rates of unimolecular reactions are independent of collision frequency can be explained on the basis of the simple collision hypothesis or the radiation hypothesis. The elaborated collision hypothesis is able to explain them on the assumption of a time-lag in complex molecules between activation and decomposition. In this way a single molecule can collect energy from many successive collisions and store up a sufficient amount for activation. Just because a given hypothesis accounts for the facts, is no reason to consider that the hypothesis has been proved. There may be other hypotheses which will account equally well for the facts. The hypothesis of chain reaction offers a competing hypothesis which up to the present time has been increasing in favor. 

The first attempt to resolve this problem was the radiation hypothesis of Perrin [1], in which the molecule is assumed to be energized by absorbing thermal radiation (in the infra-red) emitted by the walls of the vessel. However it was rapidly realized that the intensity of thermal radiation was quite insufficient to explain the observed rates of reaction [2], although interestingly, under conditions of extremely low collision frequency in interstellar space, Perrin s radiation mechanism is now believed to be significant [3]. 

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