384 PHENOMENA, ATOMS, AND MOLECULES 



In deriving Eq. (70) we considered the rate at which atoms in the 2nd 

 layer move to and drop into holes in the ist layer. It is, however, possible, 

 because of the mobility in the ist layer, for holes in the 1st layer to move to 

 atoms in the 2nd layer. Considerations like those used in deriving Eq. (69) 

 lead to the conclusion that the diffusion coefficient for holes is the same as 

 for atoms and that the surface flux of holes as well as that of atoms is given 

 by the last member of Eq. (69). Taking Eq. (70), after eliminating cp2 

 byEq. (69), 



P = Sai'iD2 + diD{){l~d,)d2il-e2). (71) 



The values of p given in Table V were obtained by this equation, with 

 the data for Do given by Table VI. They are large compared with pi or v 

 and therefore the surface phase postulate applies. 



