PHOTOREDUCTION OF CHLOROPHYLL
June 5, 1963
1571
t o 2.5 X lo-’” mole/cc., are very much less than the other products involved in the cross-combination ratio. An interpretation of the pre-exponential ratio A a b / ( A a a A b b ) ’ ” obtained in this work is not obvious, and no theoretical relationship is expected if the steric CFs + CHaCOCHa +CFIH + CHzCOCHs factor for the sum of mutual disproportionation plus is 6.9 f 0.1 k ~ a l . / m o l e ,assuming ~ E = 0 for CF3 combination for some radical species is much less radical recombination. than unity.20 The ratio of the collision numbers &,/ Discussion (Zaazbb)’” = 2.97, Using Values for the collision diameters of U C H ~= 3.5Ai.,C C F ~= 4.0 A. and U C ~ F , = Other values of cross-combination ratios involving 6.5 A. This gives the ratio of the steric factors, Pab/ simple alkyl and peduoroalkyl radicals are unreliable, (Pa
