KINETIC AND MECHANISTIC STUDIES OF THE REACTIONS OF CF3O RADICALS WITH NO AND NO2

The reactions of CF3O radicals with (1) NO and (2) NO2 were studied us ing two different experimental techniques. A laser photolysis/LIF dete ction method was applied for measuring the rate constants as a functio n of temperature (T=222-302 K) and total pressure (p(tot)=7-107 mbar). Whereas the reaction with (1) NO was found to be independent of tempe rature and pressure with k(1)=(4.5+/-1.2)x10(-11) cm(3) s(-1), the rea ction with (2) NO2 was found to be dependent on both of these variable s. The temperature dependence of k(2) in the high pressure limit can b e given by the expression k(2,infinity)(T)=(8+/-5)x10(-13) exp ((863+/ -194) WT) cm(3) s(-1). The product distributions of the two reactions were determined in separate experiments using steady-state photolysis combined with FTIR spectroscopy. For reaction (1) only CF2O was found as a reaction product with a yield of 0.93+/-0.10, independent of temp erature. For reaction (2) several products (CF3ONO2, CF2O, FNO2) were identified, the overall yield, however, is dominated (greater than or equal to 90%) by the recombination product CF3ONO2. A theoretical anal ysis of the detailed mechanisms of both reactions was made by performi ng ab initio energy and geometry predictions in combination with RRKM calculations. Both reactions were found to proceed via an initial addi tion mechanism involving the CF3ONOx (x=1,2) intermediate and a four-c enter transition state. A direct abstraction of an F atom by NO or NO2 can be excluded.