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 [ $\mathrm{H}({\mathrm{CH}}_2{)}_n\mathrm{H}$, with $n=5\mathrm{}$ 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 $\nu {=10\mathrm{}}^{19.6\pm 0.5}{\sec }^{-1\mathrm{}}$ 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 $\Delta E_{\mathrm{des}}^{‡}{=A+Bn}^{\alpha }$, with the exponent $\alpha =0.50\mathrm{}\pm 0.01$.