NOTES
1775
Table I : Rate Constants (l./mole-sec.) for CF2 a t Room Temperature Source of CFz
Photolysis of CzF4 Hg sensitization of C Z F ~ Photolysis of CFZHBr, CFzBrs Glow discharge of CF4 O( *P) GzF4 Photolysis or pyrolysis of CFzNa
+
io4
...
Dalby’s system and is presumably the singlet. Spin conservation rules predict that of the two CF2 species formed from each C2F4-Hg(3P)collision, one should be singlet and one triplet. Apparently, the spin conservation rule does not apply in this system. Professor George Hammond of the California Institute of Technology has suggested to us the possibility that the triplet C2F4 molecule passes through excited vibrational levels of a singlet state before dissociating, and thus only singlet CF2 is formed.
Photolysis of CF2HBrand CFzBr2 CF2Br2and CF2HBr were photolyzed,5 and the absorption spectrum of CF2was observed. The addition of a large excess of oxygen did not reduce the intensity of the bands; presumably singlet CF2was present.
Glow Discharge of CF, CF2 has been produced from an electrodeless discharge of CF4 vapor, and the emission bands,6 as well as the absorption bands,’ were measured. From these optical observations, it was concluded that the species involved was nonlinear singlet CF2. In other experiments with discharged CF4,*ethylene was added downstream, and the products of the reaction were collected and analyzed. With as little as 5 or 10 p of c2H4, the C3 adducts of CF2 to C2H4were found, and their concentrations did not increase with additional C2H4. Under these conditions, the CF2 radical concentration was about 0.1 p in the absence of C2H4. Consequently, could be computed to be at least lo7l./mole-see., or lo4 times faster than that expected for singlet CF2. I n addition, the reaction with C2H4 produced chemiluminescence which reached a maximum value with as little as 5 p of C2H4. The luminescent state had a long lifetime and presumably corresponded to a triplet molecule, as would be expected if the CF2reactant were a triplet. Additions of small amounts of air between the discharge and the C2H4 inlet caused the chemiluminescence t o vanish, thus indicating scavenging of the precursor or the luminescing species, or both. It is difficult for us to understand these results unless triplet CF2 is present.
ko2
kC2%
k W d
