121 



COLLIS 

 OEACTI 

 TO 6R0UN 



DECOMPOSITION 



Fig. 4. Schematic Potential Curves for Photoreactivation Model. 



"pallative" irradiation occur within the life of state_A_. How rapidly must the 

 ultraviolet irradiation follow the irradiation by high-energy irradiation in order 

 to have this protective effect? 



MAZIA: As much as a day. 



MAGEE: That is not impossibly long. You can have some odd configuration 

 of a molecule. You remember I mentioned linear H2O. You go to such a state 

 and not the ground state of the molecule, and there can be a large barrier for 

 going back. 



KASHA: I think there are two things which tend to be confused here. I 

 would say that there can be a geometrical isomer (which may or may not be a 

 triplet) which radiates down in some instances, but if the geometry is extreme- 

 ly different it may not ever radiate down. 



