Energy-Transfer Cross-Section

Figure 14.6 Fin of constant cross-sectional area transferring energy by radiation and convection.

The cross sections of transfer, diffusion, and total elastic scattering were obtained and are illustrated as functions of incident energy in Figs. 4-6. 

The capabilities of fluorescence spectroscopy can be enhanced by using the methods of laser fluorimetry, in particular nonlinear laser fluorimetry (Fadeev et al., 1999). This method allows one to get information on the molecular level and deterrnine the photophysical parameters of molecules (absorption cross section, lifetime in excitation state, intersystem crossing and energy transfer rates, etc.). Furthermore, the p>arameters can be measured in vivo and in situ in the absence of a priori information, which is necessary for conventional spectroscopic methods (for example, molecular concentration (Banishev et al., 2009)). 

Elastic differential cross sections follow from the TCF for elastic phenomena. Integrating the double differential cross section over transferred energies, we obtain... 

We start from a model in which collision cross sections or rate constants for energy transfer are compared with a reference quantity such as average Leimard-Jones collision cross sections or the usually cited Leimard-Jones collision frequencies [54]... 

Here t. is the intrinsic lifetime of tire excitation residing on molecule (i.e. tire fluorescence lifetime one would observe for tire isolated molecule), is tire pairwise energy transfer rate and F. is tire rate of excitation of tire molecule by the external source (tire photon flux multiplied by tire absorjDtion cross section). The master equation system (C3.4.4) allows one to calculate tire complete dynamics of energy migration between all molecules in an ensemble, but tire computation can become quite complicated if tire number of molecules is large. Moreover, it is commonly tire case that tire ensemble contains molecules of two, tliree or more spectral types, and experimentally it is practically impossible to distinguish tire contributions of individual molecules from each spectral pool. 

The pulsed-plate column is typically fitted with hori2ontal perforated plates or sieve plates which occupy the entire cross section of the column. The total free area of the plate is about 20—25%. The columns ate generally operated at frequencies of 1.5 to 4 H2 with ampHtudes 0.63 to 2.5 cm. The energy dissipated by the pulsations increases both the turbulence and the interfacial areas and greatly improves the mass-transfer efficiency compared to that of an unpulsed column. Pulsed-plate columns in diameters of up to 1.0 m or mote ate widely used in the nuclear industry (139,140). 

Isothermal Gas Flow in Pipes and Channels Isothermal compressible flow is often encountered in long transport lines, where there is sufficient heat transfer to maintain constant temperature. Velocities and Mach numbers are usually small, yet compressibihty effects are important when the total pressure drop is a large fraction of the absolute pressure. For an ideal gas with p = pM. JKT, integration of the differential form of the momentum or mechanical energy balance equations, assuming a constant fric tion factor/over a length L of a channel of constant cross section and hydraulic diameter D, yields,... 

Jameson C. J., Jameson A. K., Smith N. C. 15N spin-relaxation studies of N2 in buffer gases. Cross-sections for molecular reorientation and rotational energy transfer, J. Chem. Phys. 86, 6833-8 (1987). 

The production of N02 by charge transfer from either SF6 or SF5 , previously observed by Curran (4), has been confirmed during this work. The attachment cross-section curves for SF6 and for SF5 closely overlapped in the low energy range, and it was impossible to determine whether SF6 or SF5 was the reacting ion. 

That is, if one compares the cross-sections at the same kinetic energy E of the incident ion, the transfer of a H atom always occurs with a larger cross-section than the transfer of a D atom. (The cross-sections at the same relative kinetic energy are equal since the effective radial potential in which the particles move during the collision is the same for H- and D-atom transfer. The effective potential is the sum of the potentials... 

Reactions of Complex Ions. For reactions of systems containing H2 or HD the failure to observe an E 1/2 dependence of reaction cross-section was probably the result of the failure to include all products of ion-molecule reaction in the calculation of the experimental cross-sections. For reactions of complex molecule ions where electron impact ionization probably produces a distribution of vibrationally excited states, kinetic energy transfer can readily open channels which yield products obscured by primary ionization processes. In such cases an E n dependence of cross-section may be determined frequently n = 1 has been found. 

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