R. Atkinson (J. Phys. Chem. Ref Data 26,215 (1997)) has reviewed a large set of rate constants relevant to the atmospheric chemistry of volatile organic compounds. The recommended rate constant for the bimolecular association of O, with an alkyl radical R at 298 K is 4.7 X 109 dm mol-3 s-J for R = C2Hs and 8.4 x 109 dm3 mol-1 s-1 for R = cyclohexyl. Assuming no energy barrier, compute the steric factor, P, for each reaction. (Hint Obtain collision diameters from collision cross-sections of similar molecules in the Data section.)