Atomic reaction cross-sections

Notice the de Broglie wavelength of thermal neutrons is much larger than the size of a typical nucleus (r 1-10 x 10-15 m) and similar to the size of a typical atom. Reaction cross sections for thermal neutrons exceed the geometrical area of the nucleus. 

Endothermic Reactions and the Determination of Bond Dissociation Energies for Organometallic Fragments. The reaction of atomic nickel ion with molecular hydrogen to yield NiH+is substantially endothermic. Reaction cross sections for this process, measured using the ion beam apparatus shown in Figure 1, are displayed in Figure 3 for reactions 1 and 2 with HD as the neutral. 

Harpoon reactions of alkaline metal atoms with halogen molecules in the gas phase seem to be the first instance of the observation of chemical electron transfer reactions at distances somewhat exceeding gas-kinetic diameters. Actually, as far back as 1932, Polanyi, while studying diffusion flames found for these reactions cross-sections of nR2, somewhat exceeding the gas-kinetic cross-sections [69]. Subsequently, more precise measurements which were carried out in the 1950s and 1960s with the help of the molecular beam method, confirmed the validity of this conclusion [70],... 

This alkalilike behavior of metastable noble-gas atoms effectively transforms the excitation energy of the metastable noble-gas atom into electronic energy of a rare-gas halide molecule with large reaction cross section. Because the electronically excited noble-gas halides have short radiative lifetimes and the ground-state noble-gas halides are not strongly bound, the process of formation of electronically excited noble-gas halides from metastable noble-gas atoms has been shown to be ideal for the operation of the electronic transition laser and has been successfully used in high-efficiency rare-gas halide lasers in recent years.21"23... 

Scattering of Noble-Gas Metastable Atoms in Molecular Beams velocity. The total reaction cross section is... 

All these contributions add up to a total antihydrogen formation cross section of approximately 2 x 10-15 cm2 in the antiproton energy range 2-10 keV where the charge-exchange production mechanism is likely to be most effective. This value is consistent with results obtained by Ermolaev, Bransden and Mandal (1987), who used the classical trajectory Monte Carlo method, and also with the results of a recent experiment (Merrison et al., 1997) which measured the hydrogen atom formation cross section via reaction (8.22). 

A few words on the form of P, (p) are in order. Our opacity is very different from that often encountered in textbooks of gas phase reactions, where P, is assumed to be constant up to some value of p, and zero beyond that. Similar holes (regions of low reactivity at low p) in the opacity function have been computed for the ER reactions of H(g) with Cl adsorbed onto Au( 1 1 1) [91,92] and with H physisorbed onto graphite [85]. For H atoms on a corrugated Cu(l 1 1) surface we find smaller holes than in Fig. 4, but the reactivity still becomes small near zero impact [38]. Note that the reaction cross section, defined as... 

The kinetics are determined by a few intuitive parameters which can be extracted from our quantum or QC studies, estimated, and in some cases, measured. Ignoring isotope effects, the parameter set reduces to Prs,c = Cxx = cxY,r = p/s = rxx = rxx = rxx = > yy and b = bXY. Our QC simulations suggest that p is small for H and D atom reactions on the order of 0.1 for Ni(l 00). The ER reaction cross sections are also small on the order of 0.5 A2, or less. We have observed b to be on the order of a few to several percent, and to be isotope dependent, with D more likely to knock an adsorbed H out of its site than the other way around. 

Figure 16 Reaction cross section, cr, and average HD rotational and vibrational quantum numbers, ( /) and (n), respectively, as a function of the incident energy, for H incident on an initially chemisorbed D atom, for the relaxed lattice case. Taken from Ref. [71],...

Greene, Ross, and their co-workers [15,40] have found the following total reaction cross sections for reactions of K atoms with hydrogen halides ... 

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