Cross-Sections and Rate Coefficients

Collisional ionization can play an important role in plasmas, flames and atmospheric and interstellar physics and chemistry. Models of these phenomena depend critically on the accurate detennination of absolute cross sections and rate coefficients. The rate coefficient is the quantity closest to what an experiment actually measures and can be regarded as the cross section averaged over the collision velocity distribution. 

The END equations are integrated to yield the time evolution of the wave function parameters for reactive processes from an initial state of the system. The solution is propagated until such a time that the system has clearly reached the final products. Then, the evolved state vector may be projected against a number of different possible final product states to yield coiresponding transition probability amplitudes. Details of the END dynamics can be depicted and cross-section cross-sections and rate coefficients calculated. 

A new R-matrix approach for calculating cross-sections and rate coefficients for electron-impact excitation of complex atoms and ions is reviewed in [307]. It is found that accurate electron scattering calculations involving complex targets, such as the astrophysically important low ionization stages of iron-peak elements, are possible within this method. 

Cross-sections and rate coefficients for electron impact recombination (25 785 sets). 

In order to evaluate DSMC chemistry models, we require experimental and/or detailed theoretical results. Data of interest that can be measured experimentally include reaction cross sections, and rate coefficients. The most useful type of theoretical data are generated by detailed analysis of the collision and reaction dynamics using potential surfaces obtained from high level quantum chemical methods. 

MICROSCOPIC REACTION CROSS-SECTION AND RATE COEFFICIENT... 

In the case of large molecules, instead of the detailed quantum state characterization implied in the cross sections and rate coefficients of the master equation (A3.13.24). one derives more coarse grained... 

Anyone who performs plasma chemistry modeling recognizes that cross sections and rate coefficients for an individual process are rarely used in isolation rather, they are generally used as part of a model involving a number of other processes. An example of this can be seen in the schematic model for C2F6 plasma chemistry shown in Fig. 1. While not much is known about C2F6 plasma... 

This is a very simple procedure that enables the reaction cross sections and rate coefficients to be determined simply by a small number of matrix dlagonalizations. Furthermore, by applying an approximation such as the centrifugal sudden approximation (CSA) in which the coupling in the projection quantum numbers of the rotational basis sets is neglected [11], the rotationally adiabatic potential curves for J > 0 are obtained from those calculated for J = 0 simply by adding the centrifugal term of equation (3). 

In this section we, first of all, compare various calculations for ion-dipole reaction cross sections and rate coefficients, and then go on to make several comparisons of theory with experimental data. 

Gerlich D. (1989) Reactive scattering of N - - H2 and deuterated analogs Statistical calculation of cross sections and rate coefficient. J. Chem. Phys. 90 3574-3581. 

T. Fujimoto, Semi-empirical cross sections and rate coefficients for excitation and ionization by electron collision and photoionization of Helium, Institute of Plasma Physics Report, IIPJ-AM-8, Nagoya University, Nagoya, Japan, 1978. 

H. Deutsch, K Becker, G. Senn, S. Matt, and T. D. Mark, Calculation of cross sections and rate coefficients for the electron impact multiple ionization of beryllium, boron, carbon, and oxygen atoms, International Journal of Mass Spectrometry, vol. 192, no. 1—3, pp. 1—8, 1999. 

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