Sticking probability dissociative

The low probability for dissociative adsorption of HCOOH on Ag is clear indication that adsorption was activated. For such a process, one would expect the dissociative sticking probability to depend on the structure of the surface, since alignment of the O-H bond with the metal surface... 

Figure 1 Hydrogen dissociation on Cu(l 1 0) [12]. The initial dissociative sticking probability Sq is measured as a function of incident translational energy E. Measurements are made by increasing die nozzle temperature Ta ( ), and by seeding at constant nozzle temperature (Tn = 1100 K) ( ). The latter measurement provides a measure of die translational energy onset (ca. 125 meV)...

Figure 2 The initial dissociative sticking probability for D2 on Cu(l 1 1) extracted from the state selected measurements of desorbing molecules for various vibrational (A) and rotational (B) states of the molecule [19]. Vibrational energy couples effectively to the reaction coordinate, lowering the translational energy requirement for dissociation. Rotational energy initially hinders and then promoted dissociation. Similar effects of rotational energy are predicted in the trajectory calculations shown in (C) for molecules constrained to rotate in a plane perpendicular to the surface [29].

However, even at low coverages on the Fe(lll) face, where the most recent studies show an activation energy for the dissociation process of -3.4 kJ mor , the dissociative sticking probability is still only 2 x 10 This reflects, in the first instance, the low sticking probability of the molecularly adsorbed species, which at approximately 10 is considerably lower than that observed for... 

K on the W(IOO), (310), and (210) planes, respectively (equivalent to desorption activation energies of approximately 314 kJ moP, although adsorption does not apparently occur on the close-packed planes such as W(llO). The high heats of adsorption are associated with high dissociative sticking probabilities of between 0.24 and 0.37 at low coverages. 

Figure 12.3 Dissociative sticking probability Sd vs. normal component of the translational energy of the incident D2 molecules in a given initial vibrational and rotational state incident on a Cud 11) surface [adapted from H. A. Michelsen eta .,...

Fig. 4.6). The standard way of improving a potential is to make the fitting to a set of ab initio points or perhaps to data such as vibrational frequencies, which are easily calculated from the potential. Then this quess is used in a dynamical calculation and, for instance, the barrier is modified to bring agreement with experimental data on sticking probabilities. However, the direct dynamical fitting may be feasible instead of this trial-and-error methodology. Certainly this would be the case if the dissociative sticking probability was calculated by transition state theory or any other simple dynamical method which would allow a fast and reliable calculation of it.

---