Differential energy distributions in nonthermal systems: Model calculations and applications to 18 F‐for‐F nuclear recoil substitutions in CH 3 CF 3

A general method has been developed for the determination of the differential energy distribution in nonthermally activated reacting systems. A series of known distributions and kinetic models has been used to test this method and to determine its efficacy. Application was then made to the kinetic data of energetic CH 3 CF 2 18 F formed by the substitution of F by 18 F produced by nuclear recoil. The distribution obtained for this activated CH 3 CF 2 18 F is seen to be highly energetic with a median energy of 137.6 kcal mol −1 and with 33.1% of the molecules possessing energy in excess of 171 kcal mol −1 . The shape of the calculated distribution suggests that there are two mechanisms for the formation of CH 3 CF 2 18 F from CH 3 CF 3 and 18 F, as well as that 62 kcal mol −1 is a lower limit to the kinetic energy needed by the 18 F atom for this substitution to take place.