Deexcitation cross sections

The deexcitation cross-sections are dependent on electronic states of excited rare gas atoms and target molecules. They are compared in detail with related theoretical results to find some regularities of cross-section values in correlation with fimdamental parameters of target molecules, from which unknown cross-section values for any molecules can be estimated with enough accuracy. Availability of this estimation will be of great importance in finding new candidates of host molecules in reactive-plasma research. 

Fig. 1. Relation of deexcitation cross sections with Eq. (1) for He(2 S) (Yoshida et ai, 1992b).

Deexcitation Cross Sections of He(2 S) by CH4, SiH4 or GeH4 IN Comparison with the Respective Cross Sections FOR Products Formation (in Units of A )... 

A little more complicated system is the de-excitation of He(2 P) by Ne, where the deexcitation is dominated by the excitation transfer and only a minor contribution from the Penning ionization is involved. The experimental cross section obtained by the pulse radiolysis method, together with the numerical calculation for the coupled-channel radial Schrodinger equation, has clearly provided the major contribution of the following excitation transfer processes to the absolute de-excitation cross sections [151] (Fig. 15) ... 

As a brief conclusion of this section, the cross-section measurements for the deexcitation of excited rare gas atoms have been best performed using the pulse radiolysis method. The pulse radiolysis method has provided not only the most reliable cross sections... 

The experimental methods used in excited-state studies are not described specifically within this chapter. Some of these techniques are referred to in Table 2 of ref. 1. Others can be found in the associated chapters in this review. Special mention should be made of material contained in a review on excited nitrogen by Wright and Winkler [2], Elsewhere in the present chapter, Section II examines the lifetimes and energies contained in the various excited atmospheric species, and in Section III some excitation and deexcitation results for the more important atmospheric species are presented. In Section IV a more complete list of pertinent rate constants and cross sections is given. 

Excitation and Deexcitation Rate Coefficients or Cross Sections ... 

Fig. 7.6. Partial cross sections in the doubly-excited spectrum of He. The total cross section is shown in the top spectrum, and the partial cross sections in the lower spectra. Note how, although the energies and widths of the resonances are the same, their shapes depend markedly on the deexcitation channel (after A. Menzel et al. [332]).

T.S. Jensen, V.E. Markushin, CoUisional deexcitation of exotic hydrogen atoms in highly excited states. 1. Cross-sections, Eur. Phys.. D 21 (2002) 261-270. 

In hot-fusion reactions, the cross section for producing heavy-element nuclides is determined by the probability that the highly excited compound nucleus will avoid fission in the deexcitation process. Cold fusion near the reaction barrier is qualitatively different the formation of the compound nucleus comes about in two separate steps [105, 107]. The reacting nuclei come into contact, captured into a dinuclear configuration, which is separated from an equilibrated compound nucleus by a potential-energy barrier which is not reproduced by the one-dimensional Coulomb-barrier model [94, 95, 210, 219, 220]. This extra barrier diverts the trajectory of the reaction through multidimensional deformation space toward quasifission, making reseparation much more likely than complete fusion. 

Besides the effect of shell stabilization in the entrance channel on the of the compound nucleus, the mechanism of " Ca-induced hot-fusion reactions shares another aspect of the character of cold-fusion reactions. While deexcitation of the hot compound nuclei is dominated by the competition between fission and neutron emission, attempts to reproduce the evaporation-residue cross sections by a simple r /ry treatment results in values that are much higher than those that are observed experimentally [300-302]. It is necessary to invoke a significant dynamical hindrance to fusion and a two-step mechanism [303, 304] to reproduce the cross sections for " Ca-induced reactions that result in transactinide nuclides [305, 306], which increases as the atomic number of the target nuclide increases. Like the cold-fusion reaction intermediate, the reaction trajectory from nuclei in contact to a compound nucleus can be diverted into a more probable path leading to quasifission, even though the potential energy of the compound nucleus is lower than or approximately equal to that of the reacting nuclei in contact [8, 105,123,174,220, 301, 307-312]. Only a small number of dinuclear intermediates reach the compact shape associated with the compound nucleus. 

Evaporation residues arising in complete-fusion reactions between actinide targets and radioactive-beam particles are controlled by the same < r /Ff > and dynamical hindrance effects as are the reaction products from stable-ion beam irradiations. It has been observed that fusion cross sections for reactions with neutron-rich radioactive beam particles can be enhanced over those with stable-isotope beams at the same Z, possibly due to an effective lowering of the fusion barrier with the increasing neutron number of the projectile facilitated by neutron flow in the dinuclear reaction intermediate [226, 454, 458]. It is unclear how dynamical hindrance effects and a reduced resistance to deexcitation by fission at high excitation energies in heavier systems will influence the formation of evaporation residues. It has been suggested that the formation of products at the... 

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