Gas phase kinetics of atomic species reactions with halocarbon free radicals at room temperature
The absolute rate constants for the reactions of CF{sub 3}, CF{sub 2}, CF, and CHF radicals with atomic oxygen, nitrogen and hydrogen have been measured in a gas flow system with photoionization mass spectrometry detection. CF{sub 3} radicals were produced by dissociation of C{sub 2}F{sub 6} or CF{sub 3}Br; CF{sub 2} radicals were produced by dissociation of CF{sub 2}Br{sub 2} or CF{sub 2}HCl; CF radicals were produced by dissociation of CFBr{sub 3} or CH{sub 2}FCl and CHF radicals were produced by dissociation of CH{sub 2}F{sub 2}, CH{sub 2}FCl and CHF or CHFBr{sub 2} in a radiofrequency discharge. CHFBr{sub 2} proved unsatisfactory as a precursor for CHF in kinetics studies in a radiofrequency discharge. Atomic reactants were produced by dissociation of the elemental gases in a microwave discharge. The pressure was 1.7 Torr. The rate constants at 293 K are 3.1 x 10{sup {minus}11} for CF{sub 3} + O; 1.8 x 10{sup {minus}11} for CF{sub 3} + N; 3.4 x 10{sup {minus}12} for CF + N; 1.2 x 10{sup {minus}11} for CF + O; 7.2 x 10{sup {minus}12} for CF{sub 2} + N; 2.0 x 10{sup {minus}11} for CF{sub 2} + O; 9.1 x 10{sup {minus}11} for CF{sub 3} + H; 3.9 x 10{sup {minus}11} for CF{sub 2} + H; 1.9 x 10{sup {minus}11} for CF + H; 4.9 x 10{sup 10} for CHF + H; 2.4 x 10{sup {minus}11} for CHF + N; and 1.4 x 10{sup {minus}10} for CHF + O in units of cm{sup 3} molecule {sup {minus}1} sec {sup {minus}1}. The reaction products that were observed are consistent with a fluorine atom displacement mechanism for nitrogen and oxygen reactions. Hydrogen fluoride was detected as the principal stable product in hydrogen reactions. The mechanisms of fluorine atom abstraction is discussed for hydrogen reactions. CHF radicals reactions appear to proceed by an association-elimination mechanism.
- Research Organization:
- Boston Coll., Chestnut Hill, MA (United States)
- OSTI ID:
- 111307
- Country of Publication:
- United States
- Language:
- English
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