Fig.7. Energy profiles
for the reaction of CF3I+OH obtained at the
B3LYP/LanL2DZ level.
Similar to the reaction of the OH radical with CF3I
discussed above, the reaction of the H radical with CF3I
can also produce three different products when they are close to each
other. However, part of the reaction of CF3I + H is
exothermic, which may affect the fire-extinguishing effect in physical
aspects. But in the process of the reaction can produce effective
fire-extinguishing free radicals CF3·. For example,
CF3I generates CF3· + HI through the
transition state TSc2, and the energy barrier height is 22.350
kcal·mol−1. The specific transformation process is
that CF3I first dissolves one of the F atoms to form the
transition state TSc2, then the hydrogen atom attacks the I atom of
CF3I, and finally the separated F atom returns to its
original position. In the CF3I + H reaction, there is
another reaction path that H radical directly extracts fluorine from
CF3I through TSc1 to form CF2I· + HF,
and the energy barrier height is 29.074 kcal·mol−1. In
the final reaction path, hydrogen atoms directly attack C atoms, and one
of the fluorine atoms falls off to form CF2IH + F· with
an energy barrier of 8.856 kcal·mol−1.
According to the above calculation results, the potential energy curve
of the reaction path between CF3I and hydrogen is shown
in Fig.8 . The results show that hydrogen can extract I atom
from CF3I with a small energy (less than 30
kcal·mol−1), which leads to generate effective
fire-extinguishing free radical CF3·. In addition, the
reaction rate constants of each reaction path between
CF3I and active radicals at 1 atm and different
temperatures (280-2000K) are shown in Fig.9 . It can be seen
that the rate constants of the C─I bond homolysis reaction are all
higher than that of the C─F bond homolysis reaction at various
temperatures, which is consistent with the thermal decomposition
analysis of CF3I. Thus, it is further verified that C─I
bond breaks more easily than C─F bond. From the perspective of reaction
kinetics, it is shown that CF3I is easy to form I and
CF3 extinguishes free radicals, which explains the good
extinguishing performance of CF3I.