124 ELEMENTARY CHEMICAL PROCESSES 



Some Important Aspects of the Elementary Physical 

 Processes 



For practical purposes, of course, organic compounds of interest to 

 the radiobiologist are rarely pure. Mostly, they are . dissolved or sus- 

 pended in water. Consequently, consideration of the reciprocal effects 

 of nature of the ionization process and nature of the mixture is here 

 desirable. 



effect of ionization potential and negative-ion formation 



In a mixture of possible reactants, one will have the lowest ionization 

 potential, or, since we wish some rigor and the case may be complicated, 

 a process involving one of them will yield a positive ion at a lowest energy 

 level. Schematically, we may say that in a mixture A, B, C, etc., a 

 process such as 



A -^ A+ 4- e 



or 



A -^ D+ + E + e 



proceeds at minimum energy. In aqueous systems, because of the high 

 solvation energy of the H+ ion, the process involving ionization of the 



H2O (aq) -^ H3O+ + OH + e (18) 



requires only about 7.4 ev at a maximum.* This value is quite low, 

 perhaps lower than that for any process involving ionization of an organic 

 compound dissolved or suspended in water. An accurate statement 

 cannot be made because the only available data (25) refer to the gaseous 

 state of relatively simple "complex molecules." 



It can be said that irrespective of the primary ionization process in a 

 mixture of gases the ionization is with high probability transferred to 

 that entity ionization of which requires the minimum energy. 



In liquid mixtures, such as those of interest to the radiobiologist, 

 water preponderates. It is most likely to be ionized in the first instance 

 simply because its mass concentration so much exceeds that of any solute 

 or suspensoid. Any solute molecule or suspended particle is practically 

 constantly in collision with the ambient water. Thus, even if the primary 

 process involves ionization of such an entity, we may expect that the 

 resultant effect may be very much as if only the water molecule had been 

 primarily affected. 



* Calculated from data of F. R. Bichowsky and F. D. Rossini (23) and O. K. 

 Rice (24). 



