94 CHEMICAL REACTIONS IN THE GAS PHASE 



35. Mott, N. F., and H. S. W. Massey, The Theory of Atomic Collisions, Second Ed., 

 Oxford, 1950. 



36. Kassel, Louis S., Kinetics of Homogeneous Gas Reactions, American Chemical 

 Society Monograph, Chemical Catalog Co. 



DISCUSSION 

 Burton : 



It is important to emphasize the tremendous gap which separates such funda- 

 mental studies of isolated molecules as that presented by Eyring, and an 

 understanding of reactions in condensed phases, which include biological mate- 

 rial. In attempting to bridge this gap, if only crudely, several questions are 

 significant. What is the quantitative role of the cage effect? A molecule may 

 be in one particular cage for less than lO"^*^ sec after excitation, but the life of 

 that cage in such a case is not of immediate importance. For practical purposes, 

 the molecule is caged until it is deactivated or until it decomposes. If the latter 

 process occurs, the life of the cage thereafter is of great importance. If the 

 radicals can recombine, or otherwise interact, during a time approximating the 

 life of the cage, we have a cage effect. Otherwise, there is no cage effect and the 

 reaction with the solvent dominates. The hfe of the cage evidently depends not 

 only on the statistical behavior of the radical products and the surrounding 

 molecules but also, as Eyiing notes, on the energy with which the radicals are 

 formed. How fast does internal conversion of energy occur as compared with 

 external loss (for example, collisional deactivation)? Can a chemical reaction 

 involving an excited molecule occur? Does internal conversion of energy occur 

 fast enough so that a particular degree of freedom acquires sufficient energy for 

 rupture, or does the molecule, as it were, cool off before this happens? One must 

 consider both the rate at which heat is lost externally and the probability of 

 escape of the radicals from their cage before recombination. In the theory of 

 the radiation chemistry of solutions such factors must be considered in addition 

 to those discussed by Eyi'ing. In the case of a water molecule, caging of the 

 decomposition products need not be considered, since the hydroxyl radical and 

 ionic hydrogen primarily formed do not back-react. 



Eyring: 



Are there examples of reactions studied in both the gaseous and liquid phases 

 of water? Are the products of reactions in these two phases much the same? 



Platzman (Communicated) : 



There are no examples of aqueous reactions so studied. Radiolysis of water 

 vapor has not yet been investigated, and interest in aqueous solutions has 

 focussed on non- volatile solutes. 



Lind: 



Eyring will undoubtedly recall the classical experiments of Schoepfle and 

 Fellows in which liquid hydrocarbons were irradiated with high-speed electrons. 

 These experiments showed that the greater the branching of the hydrocarbon, 



