ABSOLUTE RATE CONSTANTS FOR THE REACTIONS OF F(P-2) WITH C2H2 AND C2H4 AT T=298 K

Absolute rate constants for the reactions of C2H2 and C2H4 with F(P-2) atoms have been measured using the discharge-flow kinetic technique c oupled to mass spectrometric detection at T = 298 K and 1 Torr nominal pressure. The results obtained were k(F+C2H2) = (6.2 +/- 1.3) x 10(-1 2) cm(3) molecule(-1) s(-1), which at low pressures is associated with the abstraction channel forming C2H + HF, and k(F+C2H4) = (2.7 +/- 0. 5) X 10(-10) cm(3) molecule(-1) s(-1), which is a measure of the total rate. Product studies were also conducted. This study represents the first direct measurements of the rate constants for both F + C2H2 and F + C2H4 reactions. A comparison between the absolute rate constants a nd previous relative rate measurements is made. Further comparisons ar e made with the rates and products of the reactions of the other halog en atoms with C2H2 and C2H4 and the reactions of the pseudohalogen CN with the same molecules. The suitability of these reactions as precurs ors for vinyl and ethynyl for discharge-flow studies is briefly discus sed.