Ig. Pitt et al., APPLICATION OF TRANSITION-STATE THEORY TO GAS-SURFACE REACTIONS - BARRIERLESS ADSORPTION ON CLEAN SURFACES, Journal of physical chemistry, 98(49), 1994, pp. 13001-13010
Transition-state theory (TST) has long been applied to gas-surface rea
ctions for the purpose of characterizing and predicting desorption rat
e coefficients. However, current perceptions of its use exclude the us
e of TST from meaningful description of the sticking coefficient, eith
er for clean or for partially covered surfaces, principally because of
the limitations of the theory in describing adsorbate-adsorbent energ
y transfer. TST has thus previously been neglected as an interpretativ
e and predictive tool fdr the temperature and coverage dependence of t
he sticking coefficient, particularly for processes without a barrier
to adsorption. It has previously been generally believed that only var
iational. minimum dividing surfaces at infinite adsorbate-surface sepa
ration could be possible for barrierless adsorption processes, implyin
g a TST sticking coefficient of unity. Reassessment of this point sugg
ests that this is not necessarily the case even for clean surfaces; a
form for the desorption rate coefficient that insists all trajectories
have sufficient energy to desorb is derived, and a model calculation
of the temperature dependence of the sticking coefficient on a clean s
urface is presented that demonstrates that other variational minimum d
ividing surfaces are indeed possible.