Kinetics and energetics of oligomer desorption from surfaces

dynamics of oligomer desorption from surfaces has been studied by measuring the desorption kinetics of a set of straight chain alkanes [H(CH2)(n)H, wi th n = 5 to 60] from the surface of single crystalline graphite. Desorption is observed to be a first-order process and the preexponent of the desorpt ion rate constant has a value upsilon = 10(19.6 +/-0.5) sec(-1) and is inde pendent of the oligomer chain length. More interestingly, we find that the barrier to desorption has a nonlinear dependence on chain length and takes the form DeltaE(des)(double dagger) = A + Bn-alpha, with the exponent alpha = 0.50 +/- 0.01.