Desorption probability

The described bioaffinity separations demonstrate that polyacrylamide spacers aid the selective binding of highly complex and delicate biomacromolecules and their associates. Moreover, these solutes remain biologically active after desorption probably due to the high inertness and flexibility of the surrounding polymer chains fixed on the solid support. The unbound parts of serum usually show no loss of the activities of their constituents. Thus we evaluate the surface of inorganic supports coated with chemisorbed iV-hydroxyethyl polyacrylamide and its derivatives as being biocompatible. 

Site-specific desorption probability SDS Sodium dodecyl sulphate... 

The extension of analytical mass spectrometry from electron ionization (El) to chemical ionization (Cl) and then to the ion desorption (probably more correctly ion desolvation ) techniques terminating with ES, represents not only an increase of analytical capabilities, but also a broadening of the chemical horizon for the analytical mass spectrometrist. While Cl introduced the necessity for understanding ion—molecule reactions, such as proton transfer and acidities and basicities, the desolvation techniques bring the mass spectrometrist in touch with ions in solution, ion-ligand complexes, and intermediate states of ion solvation in the gas phase. Gas-phase ion chemistry can play a key role in this new interdisciplinary integration. 

In addition this investigation showed that the desorption probability by recoiling of Pb-214 atoms from particle surfaces of atmospheric aerosol is 0.50 0.15. 

The low threshold energies for the production of D( S), 0( P), and 0( D2) show the importance of valence excited states in the BSD of neutral fragments [47]. The pathway for D( S) desorption probably involves D O D -I- OD. Ffowever, the thresholds for producing 0( P2) and 0( D2), which are the same within experimental error, are lower than the 9.5-and 11.5-eV thermodynamic energies required to produce 0( P2) + 2D( S) and 0( D2) + 2D( S), respectively. The low threshold values therefore indicate that the formation of 0( P2) and 0( D2) must occur by a pathway which involves simultaneous formation of D2. Kimmel et al. have in fact reported [46] a threshold for the production of D2 from D2O ice at — 6 to 7 eV, which supports this conclusion. Above the ionization threshold of amorphous ice, these excited states can be formed directly or via electron-ion recombination. 

This section introduces the principal experimental methods used to study the dynamics of bond making/breaking at surfaces. The aim is to measure atomic/molecular adsorption, dissociation, scattering or desorption probabilities with as much experimental resolution as possible. For example, the most detailed description of dissociation of a diatomic molecule at a surface would involve measurements of the dependence of the dissociation probability (sticking coefficient) S on various experimentally controllable variables, e.g., S 0 , v, J, M, Ts). In a similar manner, detailed measurements of the associative desorption flux Df may yield Df (Ef, 6f, v, 7, M, Ts) where Ef is the produced molecular translational energy, 6f is the angle of desorption from the surface and v, J and M are the quantum numbers for the associatively desorbed molecule. Since dissociative adsorption and... 

Moreover, as the system of Eq. (24) is a starting point for the cluster-type approach and the MC method, therefore in principle the two methods can be used in combination. It has been proposed by Hood et al. [297] to write down the kinetic equations for describing variations in the occupancy state of each lattice site, i.e., to abandon consideration of the lattice ensemble, and to solve the system of the equations with the dimension equal to the number of sites. The system of the connected equations has been solved numerically. In each time interval the desorption probability for a given molecule is determined by the random sampling and then the general adsorbate change found. The combination approach allows to trace the adlayer structure and to construct a correlation between the structural and the kinetic behavior of the process. Such an approach has been applied to the N2/Ru(001) system to obtain a qualitative agreement with experiment [298]. 

The mechanism for the rotation reaction has been proposed in literature to involve an alternation between the G-T)1 intermediate (Figure 1 A) and either a di-G-r)1 (Figure ID)32,41 or a 7t-T)2 intermediate (Figure 1C). However, also Dl is believed to be formed via the G-r)1 intermediate (Figure 1A), and thus the amount of Dl observed indicates the desorption probability of the G-r)1 intermediate. Since generally a (local) maximum for Dl is observed, this desorption probability is relatively high. Therefore, a rotation mechanism involving this G-r)1 intermediate should show intensities in the order D1>D2>D3>D4>D5. Since this is not the case, the rotation mechanism cannot include a G-T)1 intermediate. In addition, since the... 

The desorption probability is not influenced by the number of D-atoms in the product. 

For both supports it was found that the average number of rotations for each n-T intermediate, and, related to this, the desorption probability is unaffected by the particle size. Also for both supports, larger particles lead to an increased roll-over activity via the di-G-T]1 intermediate, whereas the contribution of the di-o-r)2 intermediate is unaffected within the limits of accuracy. 

Results of similar experiments by Gault and his co-workers (93) with a 10-wt % Pt/Al203 catalyst (mean crystallite size 150-200 A) required the assumption that several successive rearrangements took place in the adsorbed phase before desorption. A model was developed in which either a dehydrocy-clization-hydrogenolysis event or a methyl or ethyl shift involving a tertiary atom competed with desorption. By assuming that the isomeric hexanes had the same desorption probability (d) and the different bond-shift processes proceeded with the same chance (r), it was found possible to reproduce the observed initial product distributions with these two independent parameters. In general, values of d 0.5 and t = 0.10-0.20 fitted the results best. As an additional refinement, the ratio of the C2—C3 and C3—C4 bond scission probabilities for methylcyclo-pentane (0) was taken to be 3.3, rather than the statistical value of 2, to improve further the fit. 

As shown in Fig. 4 the initial adsorption probability, S0, for oxygen on Ag(l 1 0) decreases smoothly with T and goes to zero only when desorption of the atomic state becomes important. At room temperature the ratio between dissociation and desorption probability is accordingly 2 to 1 in favour of dissociation. Such ratio can only be justified if dissociation occurs also at flat terrace sites [44]. On Ag (100), on the contrary, S0 drops abruptly above T = 170 K, i.e. as soon as the lifetime of the molecular precursor becomes smaller than the typical time scale of KW experiments. Such behaviour indicates... 

The factor of 2-3 difference between the desorption probability from terrace and step sites for both NO and CO is much smaller than what is expected from the large difference in binding energy between step and terrace sites. Under equilibrium conditions at T= 3,000 K (the kinetic temperature of desorbing molecules), the... 

Based on the lower desorption probability and the shape of the 2PC spectrum (not shown), the friction model gives a three times smaller electron-coupling time (0.025 ps) for the step sites. The absolute error is significant, but the relative value (compared to terrace NO) can be determined reliably. A similar analysis of the CO data reveals an electron-coupling time of 0.3 ps and 0.1 ps for CO adsorbed on the terraces and the steps, respectively. Thus for both CO and NO the electron coupling time is three times faster at the step sites than at the terrace sites [37]. 

For rising field strength values the desorption probability of the adsorbed... 

At a first glance, cobalt and iron are similar FT-catalysts with both, waxes, diesel fuel, gasoline and LPG can be obtained. Mainly the reaction temperature controls the probability of chain prolongation pg. High values of Pg are noticed at low temperature (ca. 190 - 230°C). This corresponds to the general trend for the hydrocarbon-intermediates the increase of desorption probability with increasing temperature [16]. 

On Zirconium. AES indicated that PH3 can be adsorbed on clean Zr(OOOI) surfaces at room temperature, though only diffuse (1x1) LEED patterns were found for exposures to 10" to 10 Torr-s. Desorption, probably of PH3, started around 100 C and further desorption, probably of Hg and/or P-H-containing species, started at 360 C [35]. 

When calculating adsorption-desorption probabilities one has to use models, that allow one to couple the energetic variables in the gas phase with those in the adsorbed layer. Let us divide the translational motion of an adsorbed molecule into normal and tangential components. We shall denote the energies of the molecular motion along x, y, z eixes as Ey, E respectively. The momentum of the projectile molecule in the same coordinate system can be presented as... 

In case of multilayer adsorbate (P> 2) certmn hypotheses on the capture mechanism and interaction potential of colliding particle with the adsorbate are necessary for the calculation of the adsorption probabilities. Particularly, in some cases the expressions (7.1.6) and (7.1.7) are valid. Omitting the question of the calculation of detailed adsoi-ption-desorption probabilities let us formulate a model based on ideas of the two-layer adsorption model and BET-approximation for the adsorption isotherms of multilayer fihns (Flood 1967). The main assumptions of this generalized kinetic BET-model are ... 

The total reactive desorption probability may also be presented as a sum of the probabilities connected with different mechanisms (LH - Langmuir-Hinshelwood, D - direct) ... 

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