Kinetics and Energetics of Oligomer Desorption from Surfaces

The dynamics of oligomer desorption from surfaces has been studied by measuring the desorption kinetics of a set of straight chain alkanes [ H(CH2)nH, with 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 desorption rate constant has a value ν = 1019.6±0.5 sec-1 and is independent 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 ΔEdes‡ = A+Bnα, with the exponent α = 0.50±0.01.