TEMPERATURE AND PRESSURE-DEPENDENCE OF THE C2H4 YIELD FROM THE REACTION C2H5-2(O)

The yield of C2H4 from the reaction C2H5 + O-2 reversible arrow C2H5O2 (1) has been investigated as functions of temperature (260-530 K) and pressure (50-1500 Torr) at nonambient temperature using a relative ra te technique. This yield has a non-Arrhenius temperature dependence, i ncreasing slowly at a gas density of 4.9 x 10(18) molecules cm(-3) wit h an apparent activation energy of 1.1 +/- 0.25 kcal in the temperatur e range 250-400 K and then increasing sharply as reaction 1 becomes re versible. These results are consistent with the formation of C2H4 via rearrangement of an excited adduct (C2H5O2) with an energy barrier le ss than 1.1 cal. The yield follows a P--0.75 dependence at temperature s below 400 K. The pressure dependence becomes less pronounced at high er temperature (P(-0.32)at 529 +/- 10 K). Rate constants of the couple d mechanism for C2H4 formation developed by Wagner et al. provide reas onable agreement with these data to within the experimental error. The overall rate constant of reaction 1 was determined as a function of t emperature (260-460 K) at 580 Torr relative to that of C2H5 + Cl-2 --> C2H5Cl + Cl (3). No temperature dependence is observed in the range 2 60-380 K [k(1) = (8.1 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1)]. At 460 K, the rate constant decreases similar to 35%.