Exit channel barrier, height

The simplest dynamical model of associative desorption is based upon a one-dimensional PES with, of course, a single barrier in the exit channel for desorption (Van Wiligen 1968). (An exit channel barrier for desorption is equivalent to an entrance channel barrier for dissociative chemisorption.) Assuming an equilibrium distribution of adsorbates at the surface temperature T, the model predicts a Boltzmann distribution of velocities with the Z-component of velocity centered around v = (2Fq/M) where Vq is the barrier height. The angular distribution of desorbed molecules is then... 

There are four energy parameters in T 0) (i) the potential energy difference between the entrance and exit channels, U(—oo) (ii) the height of the potential barrier,... 

Besides the barrier height, the widths of the entrance and exit channels also count. 

Figure 5. The two-dimensional QD potential energy surface, V x,y), defined in Eq. 37. Note the entrance and exit channels, entrance and exit barriers and the QD embedded between the barriers. Parameters /ie = 1 Vb = 0.5 a = 1.6 7 = 0.1 Vp = 0 A = 0.75 Woo = 1 a = 0.76215 b = 0.32802 c = 0.08871. The parameters a, 6, c were calculated according to the geometry of the QD in Heiblum s experiment. A was chosen to allow the control on the depth of the QD well by a single parameter, Vp, without changing the height of the barriers.

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