Angle-resolved desorption

In many cases adsorption is not activated ( a = 0) and so the desorption energy is a direct measure of the adsorption heat. As discussed in the previous chapter, however, adsorption is often direct and activated, and desorption methods can be used to determine Ea. Two main types of experiment are used to measure the adsorption activation barrier — angle resolved desorption and time of flight measurements. When desorbing over a net barrier molecules enter the gas phase with excess energy commensurate with the top of the barrier. Since desorption usually involves breaking a surface-molecule bond in the reaction coordinate there is then an enhanced distribution of... 

Fig. 21. Angle resolved desorption measurements of nitrogen desorption from W( 110), upper figure, and W(310), lower figure.

Finally, some details of the dynamics of NO conversion reactions on surfaces have been recently probed by using angle-resolved TPD. For instance, in a study of the decomposition of N20 on Rh(110), Matsushima and co-workers have identified four N2 peaks between 60 and 150 K originating from direct N20-dissociation, and a fifth feature at 160 K attributed to the desorption of N2 molecules adsorbed on the surface after previous decomposition (Figure 3.2) [20]. The appearance of each of these peaks... 

Fink, A., Huber, R. and Widdra, W. Ethylene adsorption on Ge(100)-(2 x 1) A combined angle-resolved photoemission and thermal desorption spectroscopy study. Journal of Chemical Physics 115, 2768-2775 (2001). 

Ohno et al. [79] measured the angle resolved translational energy distributions for N2 formed during NO and N20 thermal desorption (Fig. 24). They found that both NO and N20 TPR gave very similar... 

R.H. Stulen. Recent Developments in Angle-Resolved Electron-Stimulated Desorption of Ions from Surfaces. Prog. Surf. Sci. 32 1 (1989). 

Matsushima, T., Angle-resolved measurements of product desorption and reaction dynamics on... 

Surface element concentrations measured at three photoelectron exit angles for water-sized and silane-treated E glass fibers are shown in Table 1. Angular resolved components of high resolution N Is and Si 2p photo peaks are displayed in Tables 2 and 3, respectively. The photoelectron exit angles correspond to penetration depths of approximately 1 nm at 15° to 5 nm at 90° [7]. Aminosilane-treated fibers were analyzed before and after ramping to 300°C in a programmed thermal desorption experiment. 

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