Thermal capture rate constants

Provided that microscopic reversibility is properly accounted for, thermal averaging of specific rate constants leads to thermal capture rate constants such that a relation between /rigid and /ngid( ,7) can be established. As the charge-dipole potential is particularly simple, the behavior is transparent such that a reference for comparison with other types of interaction potentials is available. 

It is easily shown that, in the classical limit, Eqs. (41) and (42) are consistent with the thermal capture rate constants for the oscillator model of charge-permanent dipole capture. The relevant part of the activated complex partition function, instead of Eq. (11), can be written as... 

In other words, the thermal capture rate constant of CVTST exceeds that of SACM/PST by a factor e - 2.718. The result may be somewhat improved by ICVTST, that is, by replacing Q = G( ) by Q(r, V(j, m, l, r ) > 0). Again the calculation is straightforward, giving... 

Thermal averaging of /xVTST or I/xVTST results, via Eq. (43), leads to thermal capture rate constants, with... 

WITH 18 Neutral Reactants at Thermal Energies, and also the Ionization Energies of the Reactants, the Thermal Capture Rate Constants k, and the Exoergicity for the Respective Charge-Transfer Reactions Using the Adiabatic RE(KrJ) = 12.85 eV... 

In order to later estimate thermal electron capture rate constants, Van Doren et have calculated the polarizabilities of the SF C1... 

The integration variable E in equation (26) is effectively E, ,. The condition for the validity of these equations for a thermally averaged rate constant kba(T) is the existence of a well defined Maxwell-Boltzmann distribution of velocities of collision partners or relative collision energies (E — a) at temperature T, which remains unperturbed by the reaction process. If, furthermore the internal state distributions of the reactants also remain at an unperturbed Boltzmann distribution at temperature T, one finds a thermal rate constant for complex formation (or capture ) given by equation (28) ... 

Figure 3. Thermal rate constants for capture of HC1 by H3 (PST locked-dipole capture corresponding to phase-space theory, Eq. (16) SACM statistical adiabatic channel model, Eqs. (26)-(34) [15] SACMci classical SACM, Eqs. (28H31) [15] CT classical trajectories, Eqs. (26) and (27) [1]).

Figure 10. Thermal rate constants for capture of N2 by an ion (SACM calculation [33] with channels generating from rotational states N = 0, 1,2, accounting for nuclear statistical weights left figure positive ion right figure negative ion).

The electron e generated by irradiation via ionization of the molecules of the medium S is thermalized (et ) and then is either captured by a trap, T (rate constant k ) to yield et or reacts with an acceptor, B (rate constant k2). Scheme (24) leads to a linear dependence of the value of G"1 on the acceptor concentration... 

Here X is a surface state that is occupied by an electron and is therefore able to capture a hole. Xf is the vacant state created that is now able to accept an electron from the conduction band. The surface concentration of X will depend on the total surface density of surface states and their electron occupancy. The rate constants for hole and electron capture, (3p and f can be defined as the products of the thermal velocities, vp and v and the capture cross sections ap and tr of X and X+. 

The recombination rate constant k°ec(U = UFB) can be expressed as the product of the doping density Nd, the thermal velocity v of electrons and the electron capture cross section tr of X+ ... 

The rate constant for the capture of low energy (thermal <1 eV) electrons by COClj has been measured by electron cyclotron resonance (e.c.r.) as 5 x 10 cm s [1817]. Thus, phosgene is a much more effective electron scavenger than dichlorine or chloroalkanes. The process of electron capture is believed to be [1817] ... 

Other experimental procedures measure the energetics and kinetics of thermal electron reactions in the same manner as the ECD and NIMS. These are designated equilibrium methods. The direct capture magnetron method (MGN) and the individual determination of the individual rate constants k and k- for thermal electron reactions are also equilibrium methods. The latter was first carried out in an electron swarm (ES) for O2, but can be applied to any system to measure thermal electron reactions. These methods differ in how the electron and ion concentrations are generated and measured [6, 7],... 

The recombination rate constant k depends on the doping density Nj, the thermal velocity v of majority carriers and the majority carrier capture cross section a of recombination centres ... 

Dissociative electron capture also occurs at energies greater than thermal but usually with significantly lower rate constants (cross sections) and various fragmentations. For example, SFg at low energies forms a metastable molecular anion whereas at higher energies direct impact dissociation to SFj" and F occurs but with a much lower cross section. 

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