Cross sections for energy transfer

A classical molecular system, which until recently was supposed to show systematic dependence on the change in internal energy, is the collisional spin-orbit relaxation of Hg(63P) 

The magnitude of the cross-sections is not the only enigma in the mercury experiments. The second curiosity concerns the reason why the four molecules N2, CO, H20 and D20 should efficiently induce spin-orbit relaxation, whereas most other simple molecules (e.g. C02, NH3) are rather inefficient119,179. 

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Here is the total cross section for energy transfer from vibrational state i to j by collision at a relative collision velocity v andy are the equilibrium distributions of velocities of A and M. The right hand... 

In sections 1.7.2 and 1.7.3 it was shown that of all the details of individual collisional processes only the total cross section for energy transfer, CtotC o). and the mean squared energy transferred per collision, E Eg), enter into the dissociation rate constant k. Consequently we are mainly interested in determining these quantities rather than trying to describe the individual processes. 

Tables 8-12 show that the cross sections for energy transfer to states far removed from the initial state are reasonably large, so that large-Av or large-Aj transitions are not unlikely in H + H2 collisions. We also reported vibrational transitions with large quantum number changes for Ar + H2 at a collision temperature of 4500 in that study the initial rotational state of H2 was...

Figure 10. Cross sections for charge transfer from N+ to Kr as function of reactant ion energy. Triangles represent data for ground state N+(3P) and circles, for metastable N+( Z)).llb...

Figure 29. Ratio of cross section for excitation transfer followed by atomic autoionization (AAI), to total ionization cross section, as function of collision energy for systems He -Ar,Kr,Xe.77...

Abstract. Cross sections for electron transfer in collisions of atomic hydrogen with fully stripped carbon ions are studied for impact energies from 0.1 to 500 keV/u. A semi-classical close-coupling approach is used within the impact parameter approximation. To solve the time-dependent Schrodinger equation the electronic wave function is expanded on a two-center atomic state basis set. The projectile states are modified by translational factors to take into account the relative motion of the two centers. For the processes C6++H(1.s) —> C5+ (nlm) + H+, we present shell-selective electron transfer cross sections, based on computations performed with an expansion spanning all states ofC5+( =l-6) shells and the H(ls) state. 

It is obvious from Table 4.6 that the problem of excitation transfer from mercury to thallium is in a very unsatisfactory state. There is an apparent lack of consistency in the results of Kraulinya et al. (104), whose cross sections for excitation transfer to the 8 2S1/2, 6 2D2/2, and 7 2S1/2 levels in thallium seem to depend on the wavelength of the observed fluorescent component. The results of the two groups (Hudson and Curnutte and Kraulinya et al.) do not agree well with each other, and there is no consistent dependence of the measured cross sections on temperature. Finally, one would expect that the cross sections should decrease in some manner with increasing energy gap AE, but the results seem to indicate the opposite. It is manifest that considerable additional experimental work is needed to overcome these difficulties. 

O Reactions.—The cross-section for charge transfer between O- ions and 02(3Sy ) has a maximum value of 7.8 x 10-1 cm2 at an energy of 5 keV of the incident ion,289 whereas that for O- and 02(1A4,) was less than 1 x 10-1 cm2. Reaction rate-constants for reactions of O-, OH-, 02-, Cl-, C03-, and 0H-(H20) with H20 have been measured, and association rate-constants for several ions with COa and S02 tabulated.290 The rate of formation of NO+ by the reaction of 0+ with N2 has been commented upon.291 The formation of H02+ and Os+ by the reaction of 02+( 4 ) with H2 and 02 has been reported,292 and 02+-02, NO+-NO interactions have been considered.293 Rate-constants for reactions of O o4 ,) with N2, Ar, Cl, C02, H2, and 02 have been reported,294 and electron-transfer transitions during the collision of 02, N2, NO, and CO with their respective ions discussed.295 The nearly resonant process (107) has been shown not to occur with high efficiency.29 The lifetime of the 3 state of OH+ has been shown to be 900 ns.87... 

TABLE IV. Relative Cross Section for Charge Transfer of H2 with H2 As a Function of the Vibrational Energy Distribution of 112 at 430 eV Knetic Energy... 

Example 8.1 For saturation of the pump transition even moderate intensities ( p < 10 kW/cm ) are sufficient (Sect. 2.1). Assume an output power of 50 kW of the transfer laser L2 and a beam diameter of 1 mm in the focal plane, which yields /transf = 6.7 MW/cm, energy transfer cross sections of ctt 1.3 X 10 cm, which is about 1000 times larger than the gas-kinetic cross section. The energy transfer Rj = anvhvj, where n is the density of collision partners, colliding with the excited atoms. With n = 10 cm, v = 10 cm/s and hvj = 2 eV, we obtain Rj = l(f eV/s. 

AE = 0 04 eV. Compare this with the mean kinetic energy of the atoms in a gas at 450 K and make an estimate of the cross-section for excitation transfer. 

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