122 ELEMENTARY CHEMICAL PROCESSES 



or 



M + e -^ M- (116) 



A* + M (lie) 



A+ + M- < 



Other reactions ■ • 0-^d) 



, R + X (Ilia) 



A* <( 



^ B + C (III&) 



In this scheme A"*" as it reacts in reaction Ila is probably in a more stable 

 configuration than the ion in the instant of its production in step I; A* 

 is an excited molecule; M may be the same as or different from A; R and 

 X represent free atoms or radicals; B and C designate stable molecules 

 formed in one elementary act. In an interpretation of part of this 

 mechanism based essentially on a careful study of the reasonably cal- 

 culable aspects of the reactions of hydrogen, Magee and Burton (17) 

 concluded that (in those cases where reaction lib and its ensuant re- 

 actions can be ignored) the most probable path of reaction involves pro- 

 duction of free atom or radical partners Ilia, one of which is excited. 

 In the liquid state, probability of rearrangement of an excited particle 

 to yield two ultimate molecules is considerably increased (16, 17). Since, 

 of all the possible rearrangements which may occur, one usually goes by 

 an energetically lowest path, it may be expected (16, 17) and it has 

 actually been found in certain cases (19, 20) that a particular rearrange- 

 ment decomposition is so highly favored as to preclude the probability 

 of any other such process. 



In the EHT mechanism as just outlined we have omitted considera- 

 tion of possible decomposition of the ion A+ itself. Since this subject is 

 discussed in this symposium by Eyring et al, we note only that two 

 paths of decomposition are open 



R+ + X (Ifl) 



A" 



+ /■ 



\ 



B+ + C (16) 



where the letters have the significance already noted. Of the two re- 

 actions, one involving decomposition into a free radical and a free-radical 

 ion and the other decomposition into a molecule and a molecule ion, the 

 first may usually be expected to require more energy. Thus, unless the 

 initial ionization is to a point on an attractive curve above the dissocia- 

 tion limit for rupture as indicated in la, decomposition of type 16 alone 

 occurs, even though it may take a considerable time (of the order of 



