GENERATION, CONTROL, AND MEASUREMENT 133 



electron would have to fall to obtain the same energy; therefore 



eV = hc/\, 

 and 



V = hc/e\. (3-4) 



V = r2-10/X ev when X is in millimicrons. Table 3-4 gives the values of 

 Table 3-1. Quantum Energy of Various Wave Lengths of Radiant Energy 



the quantum energies at 50-m)u wave-length intervals in various com- 

 monly used units. Table 3-5 presents the number of quanta or einsteins 

 in each unit of radiant energy (Daniels, 1948). 



QUANTUM YIELD 



The need for expressing absorbed energies in quantum units stems 

 from the application of Einstein's law of photochemical equivalence, ~ 

 which states that in the primary photochemical reaction 1' quantum is 

 absorbed for each atom or molecule reacted. Thus the number of mole- 

 cules photochemically activated must equal the number of quanta 

 absorbed, and therefore the number of moles reacted must be equal to 

 the number of einsteins (moles of quanta) absorbed. The experimental 

 data for most photochemical reactions seldom show the simple one-to-one 



