r;. ]V/LSE ROBINSON 21 



termination ol the triplet state geometry has been made, vibrational 

 data in other molecides seem to confirm that singlet and triplet states 

 having the same electyoii ronfigiiration hax>e very nearly the same 

 geometrical properties. These may, Itowever, difjer greatly from the 

 geojnetry characteristic of states derived from other configurations. 

 The importance o£ the lowest triplet state of a molecule lies not in 

 its geometry, but in the fact that it is the excited state of very lowest 

 energy. Thus in any excitation process, followed by rapid internal 

 energy transfer, it is likely to be the only excited electronic state 

 Avhich retains for a sufficient time any electronic excitation energy 

 for use in chemical reactions (12) or other processes especially charac- 

 teristic of an excited electronic state. 



4. Environmental Perturbations on Electronic 

 AND Vibrational States 



Reasonably large environmental perturbations may be caused by 

 van der Waals', dipolar, or ionic fields in liquids, in solids, or in 

 gases at high pressures. In gases and liquids the perturbations must 

 be averaged over the molecular fluctuations. Intramolecular perturba- 

 tions between various parts of a molecule may be loosely classed as 

 environmental perturbations, if such perturbations remain reasonably 

 small. Because of the variations of electronic density in different 

 electronic states, an interaction with the environment affects differently 

 the various electronic states of a molecule. Since the effect on the 

 energy is different in the two combining states a shift in the spectrum 

 results. Activation energies for chemical reactions depend upon energy 

 differences between molecular states, just as spectra do, and it is 

 expected that rates of chemical reactions should generally be in- 

 creased in those cases where the spectrum is shifted to lower energy 

 (red shift) . Reactions should be slowed down in those cases where 

 the spectrum is blue-shifted. 



Non-polar solvents. Effects of non-polar neighbors are perhaps 

 the simplest to understand quantitatively, since angular dependent 

 forces, if present, are fairly small and can be neglected to a first order 

 of approximation. The potential between two spherically symmetric 

 molecules is then approximately given by the Lennard-Jones potential 

 (15), 



--&:-3 



{I) 



