J . Phys. Chem. 1984, 88, 5025-5031 Atkinson and Pitts22(2.51), Ravishankara et al.23(2.63), Nip and P a r a s k e v o p ~ u l o s(2.44), ~~ and Lorenz and ZellnerIg (3.0) an estimate of kz (298 K, M = air) = (2.7 f 0.3) X lo-" cm3 molecule-' s-l is obtained. At total pressures below 30 mbar, the k2 values differ by as much as a factor of 6. The measurements relative to the reaction C O OH CO, H20-21 have been omitted from Figure 5 , as the rate of the reference reaction subsequently proved to show a complex dependence on pressure and possibly also on the O2 partial pressure (see discussion in ref 35 for comparison). The low values of Bradley et a1.6 and Pastrana and Carr' can probably be discarded due to uncertainties in the stoichiometric factors n which they used to calculate k , from the measured nkz. Yet it is not understood why even their effective rate constants nk, are definitely low as compared to the falloff from the present work. In static experiments problems may arise from the adsorption of alkenes, and in particular of propene, on the walls of metallic reaction vessels, as has been discussed by Ravishankara et aLZ3 The low value of Stuh14 is possibly the result of such wall effects. Near 1.3 mbar, the falloff curve from the present work is in good agreement with the results of Morris et al.,3 Barnes et a1.,28and Smith,31 but only in poor agreement with the recent work of Zellner and Lorenz.lg The slight pressure dependence of k2 from this work and the much steeper pressure dependence as suggested from the work of Zellner and Lorenz are not consistent with the conclusion of Smith3' that k2 is already at the high-pressure limit
+
-
5025
near 1.3 mbar. However, the actual degree of falloff at pressures
