Attachment rate coefficients

A number of molecular species, such as NF3, HCl, HBr, HF, and N2O, exhibit strong dependence of attachment rate on temperature. This comes about because the dissociative attachment cross section increases with increasing vibrational quantum number (see Christophorou et al, 1994). This can be seen in the temperature dependence of the N2O dissociative attachment cross section shown in Fig. la, and its effect on the attachment rate coefficient can be seen in Fig. lb. The attachment cross section (Christophorou et al, 1971), where the products are NO + 0, is very temperature-dependent (Chantry, 1969), as shown in Fig. lb, which means that it is very sensitive to the degree of vibrational excitation. In a plasma, one does not need an elevated gas temperature to populate the molecular... 

Fig. 7. (a) Temperature dependence of effective dissociative attachment cross section in N2O (A) temperature dependence of dissociative attachment rate coefficient. 

There have been four quantitative measurements of the attachment cross section or the attachment rate coefficient in BCI3 since 1959 ... 

Stockdale et al. (1972) performed a measurement of the attachment rate coefficient by thermal electrons in an N2/BCI3 mixture. 

The dissociative attachment cross section as a function of electron energy a e) has a resonant stmcture. It permits one to estimate the dissociative attachment rate coefficient... 

Three-body attaehment Rate coefficient Three-body attachment Rate coefficient... 

Mayhew, C.A. Critchley, A.D.J. Howse, D.C. Mikhailov, V. Parkes, M.A. Measurements of thermal electron attachment rate coefficients to molecules using an electron swarm technique. Eur. Phys. J. D 2005,35, 307-312. 

Miller TM, Eriedman JF, Caples CM, Shuman NS, Van Doren JM, Bardaro MF Jr, Nguyen P, Zweiben C, Campbell M J, Viggiano AA. Electron attachment to sulfur oxyhalides SOE, SOClj, SOjEj, SOjCly and SO ECl attachment rate coefficients, 300-900 K. J Chem Phys. 2010 132 214302. 

Goulay F, Rebrion-Rowe C, Carles S, Le Garrec JL, Rowe BR. (2004) The electron attachment rate coefficient of HI and DI in uniform supersonic flow. J. Chem. Phys. 121 1303-1308. 

Direct adhesion of particles to fibres can be explained with Deijaguin—Landau— Verwey—Overbeek (DLVO)" " theory for soft cell particles,and the adhesion of cell particles to the fibres may be quantified by using the attachment rate coefficient, att which is related to the collision efficiency, rj, and the sticking efficiency, , as follows... 

FIG. 15 Transport rate coefficient A7 and attachment rate coefficient k ji (l-0) as a function of the adsorbed amount E for the adsorption of polystyrene from decalin on sUica using a stag-nation-point flow cell. Potymer concentration 50 g m. (Adapted from Ref. 72.)... 

By the principle of microscopic reversibility, it follows that protodeiodination must in all steps be the reverse of iodination, and since this latter reaction is partly rate-determining in loss of a proton (see pp. 94-97, 136) it follows that attachment of a proton should be rate-determining in the reverse reaction this was found to be the case, the first-order rate coefficients for reaction in H20 and 97.5 % D20 being 76.6 and 13.1 x 10"6 respectively, so that kH20jkD20 = 5.8. 

The disadvantage of the fluid model is that no kinetic information is obtained. Also, transport (diffusion, mobility) and rate coefficients (ionization, attachment) are needed, which can only be obtained from experiments or from kinetic calculations in simpler settings (e.g. Townsend discharges). Experimental data on... 

The attachment rate to the atmospheric aerosol X=0 Z, is a linear function of the particle concentration Z. Values of 5 10 3 cm3h-l for the average attachment coefficient B measured in laboratory rooms were reported by Mohnen (1969) and Porstendorfer and Mercer (1978). 

Porstendorfer, J. and T. Mercer, Diffusion Coefficient of Radon Decay Products and their Attachment Rate to the Atmosphere Aerosol, in Natural Radiation Environment III. (T. F. Gesell and W. M. Lowder, eds.), CONF-780422, Vol. 1, pp. 281-293, National Technical Information Service, Springfield, Virginia (1980). 

The cross-section for electron attachment shows an inverse dependence on electron velocity170, and for this reason there has been a marked inconsistency in the cross-sections obtained by different methods. Mahan and Young104 have reported a capture rate coefficient for thermal electrons of 2x 1014 l.mole-1.sec-1. This was obtained by a microwave technique in the presence of helium as a moderating gas. 

The rate coefficients appearing in Eqns. 17 through 19 should not be strongly temperature dependent since radical-atom and radical-radical recombination are most often either unactivated or weakly activated processes. In the case of the recombination of two surface free radicals, the rate is likely to be limited by the mobility of the polymer chains attached to the radicals. For very short chains, as are commonly produced in plasma polymerization , only those radicals which are nearest or next nearest neighbors are likely to react. If one of the radicals... 

In fact p for the acid-catalyzed hydrolysis and formation of benzoate esters is small, and since the fit to the Hammett equation is characteristically rather poor for these reactions, p is often taken as zero. Some typical values are listed in Table 16. Too much weight should not be attached to the absolute values of the reaction constants given in the table. The data do not fit the Hammett equation accurately, and it is known that much of the earlier work was subject to considerable error, because no allowance was made for the slow reaction of the catalyst with the solvent. This could affect the observed rate coefficients in three ways—by reducing the catalyst concentration, by decreasing the acid content as measured by titration, and by producing water, e.g. 

At lower altitudes where significant concentrations of ozone exist, O- ions are generated by dissociative attachment [reaction (10b)]. These electron attachment processes and the laboratory techniques used to determine their rate coefficients were reviewed some time ago by Phelps1 S4 In the stratosphere and troposphere, negative ions can also be generated by dissociative attachment reactions of thermalised electrons with pollutants1 s5,1561 such as the freons e.g. 

---