G. WILSE ROBINSON 29 



reived if it is again realized that environmental perturbations affect 

 the energy levels and electronic charge densities in a molecule. If 

 these perturbations arise Irom a rigid medium it is probable that 

 many of the molecules have rather uniform environments, so that no 

 large unsymmetrical distortions of the electron density functions are 

 realized. In fluids the perturbations are changing with time because 

 of the rapid molecular fluctuations in the local environment. Statis- 

 tically there will always be some large fluctuations which greatly in- 

 fluence the potential energy surfaces, energies, charge clouds (and 

 "mix" electronic states) , and vibrational motions of the molecule 

 and its environment. Because of the random time-dependent environ- 

 mental perturbations in fluid media, all the criteria for energy trans- 

 fer can be easily met. One can think of the molecule "scanning" 

 the fluctuating perturbations with time until just the proper condi- 

 tions are found for the non-radiative process to occur. Once the 

 crossover between electronic states has been realized, then the loss 

 to the environment of vibrational energy in the new electronic state 

 is again very rapid. 



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