p. C. WILHELMSEN, R. LUMRY AND H. EYRING 85 



Substituting this expression for k' into equation 8 gives 



^^ h 



n 

 Rearranging and taking the logarithm of this expression gives 





l - (f) ki 



h 



(11) 



The terms /c,, k, h, k, and e^st/jj either are or may be assumed to be 

 temperature independent. The plot of ln(l - <i>)/T<j) versus l/T can 

 be seen to give —AH^/R. However, in order actually to determine 

 lH\ absolute value are needed for <^ at the different temperatures. 

 These values have not been determined for the emitter in the case of 

 the chemiluminescence of luminol. However, the value obtained for 

 aH^ for small cp is proportional to the logarithm of 4>. This might 

 justify making an approximation of (^ at some particular temperature 

 and using it to calculate values at other temperatures. 



A lower limit for <^ in the case of luminol would be 0.003 which is 

 the observed overall quantum yield for the chemiluminescence of 

 luminol (Harris and Parker, 1935; Bernanose, 1951; and Bremer, 

 1953). Using this value at 20° C and making the appropriate calcula- 

 tions lead to a value of 2.6 kcal for aHK This value assumes that all 

 the luminol molecules become excited and ignores the existence of 

 side reactions. 



Another value for (f> at 20° C which might be more reasonable is 

 0.1 which is based on the observed fluorescence yields of luminol 

 (Spruit, 1950). Although the use of this value is open to the objection 

 that the emitting molecules are not the same in the two cases, the 

 molecules are probably similar and the fluorescence yield of a mole- 

 cule is essentially cj>. Values are tabulated in Table I for <^'s based on 

 <f> being 0.10 at 20° C. The use of this group of <^'s give a value of 1 

 kcal for AH*. The value of 1 kcal and the value 0.1 for <f> at 20° C gives 

 an expression 



1 1^ M 9^ 



'^"14- O.ieQTe^ooo/'^^ 



