Reaction cross section measurement

All absolute reaction cross section measurements reported in Refs. 33, 36, 40 were based on OH product detection via laser-induced fluorescence (LIE) employing the diagonal bands of the OH(A S+—A H) UV transition. However, due to predissociation of the state only the OH(u" = 0)... 

In Fig. 5, the reaction cross sections (l.O eV) and itr(2.5 eV) obtained with the new 0( P) detection approach are depicted (filled circles) together with results from earlier absolute measurements from this laboratory and relative (solid line) reaction cross section measurements. The most recent results are, within the combined error limits, in agreement with the results of the previous measurements carried out at comparable collision energies. The value obtained in the present study for... 

Apart from the electron capture reaction, the 7Be that is produced is partly consumed by proton capture via 7Be(p, a)8B reaction. Under solar conditions, this reaction happens only 0.02% of the time. The proton capture on 7Be proceeds at energies away from the 640 keV resonance via the direct capture process. Since the product 7Li nucleus emits an intense y-ray flux of 478 keV, this prevents the direct measurement of the direct capture to ground state 7-ray yield. The process is studied indirectly by either the delayed positron or the breakup of the product 8B nucleus into two alpha particles. This reaction has a weighted average 5(0) = 0.0238 keVbarn [49]. The 7 Be(p,a)8B reaction cross section measurement has been attempted both by direct capture reactions as well as by the Coulomb dissociation of 8B. For a comparison of the 5 (0) factors determined by the two methods and a critical review of the differences of direct and indirect methods, see [50]. 

Takiue, M. and Ishikawa, H. 1978. Thermal neutron reaction cross section measurements for fourteen nuclides with a liquid scintillation spectrometer. Nucl Instrum Methods 148, 157-161. 

Crossed-beam techniques and laser spectroscopic detection towards the state-to-state differential reaction cross-section measurements... 

Relative and absolute reaction cross section measurements for reaction (1) were carried out in the energy range 1.0 eV < Ec.m. < 2.6 eV. The experimental results as depicted in Fig. 4 show a pronounced maximum at Ec.m. -1.7 eV, a feature which could not be reproduced by earlier QCT calculations on different ab initio PESs [47a-e]. In quantum scattering calculations, where reaction probabilities for total angular momentum equals zero (J = 0) were calculated, it was observed that reactivity is not enhanced by either initial O2 vibrational or rotational excitation [48a]. On the other hand, it was found that reactivity markedly increases with increasing collision energy, in particular at the opening of the OH(v = 1) product channel at Ec.m. - 1.25 eV [48a]. Recently a new extrapolation mefliod was devel-... 

NRA is an effective technique for measuring depth profiles of light elements in solids. Its sensitivity and isotope-selective character make it ideal for isotopic tracer experiments. NRA is also capable of profiling hydrogen, which can be characterized by only a few other analytical techniques. Future prospects include further application of the technique in a wider range of fields, three-dimensional mapping with microbeams, and development of an easily accessible and comprehensive compilation of reaction cross sections. 

NRA as in RBS or ERDA, and possible modification of the target composition as a result of irradiation must be considered. Nuclear reaction cross-sections are also usually not available in analytical form for direct evaluation of measured data. Concentrations are, therefore, often obtained by comparison of the measured data with results from standard samples of known concentration. 

After identifying the reactant ion, reaction cross-sections were measured as a function of average reactant ion kinetic energy. Q experimental is measured for given values of (eEl) 1/2 in the spectrometer, and experimental values of k... 

Since the observation made in study of the formation HeH+ indicated that this product was not formed by reaction of He + with H2, it had been assumed that the exothermic heat of reaction of He+ ions with H2 is probably deposited in the product HeH + as internal energy, decomposing the product into H+ and He. This idea was cited by Light (16) in his phase space theory of ion-molecule reactions to account for the failure to observe HeH+ from reactions with He+ ions. The experimental difficulty in the mass spectrometric investigation of this process is that H + formed by electron impact tends to obscure the ion-molecule-produced H+ so that a sensitive quantitative cross-section measurement is difficult. 

Table I. Measured Reaction Cross-Sections for the Formation of Secondary and Tertiary Ions at E/P between 10 and 40 volts/cm.

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. 

Detailed information about specific nuclear reactions at different stages of stellar evolution and the measurement of nuclear reaction cross-sections is given (together with a good overview of the whole of astrophysics) in... 

Experiments have also played a critical role in the development of potential energy surfaces and reaction dynamics. In the earliest days of quantum chemistry, experimentally determined thermal rate constants were available to test and improve dynamical theories. Much more detailed information can now be obtained by experimental measurement. Today experimentalists routinely use molecular beam and laser techniques to examine how reaction cross-sections depend upon collision energies, the states of the reactants and products, and scattering angles. 

RAND computer 267 Rathke anion 14 raw capacitance data 164 RBS measurements 164 reaction, mechanism of 65 progress of 64 reaction cross-sections 239 reaction dynamics 209,239, 241... 

The photoionization of a molecule to yield an electron and an unfragmented ion may be considered to be the simplest of all photodissociation reactions, and therefore also one of the simplest of the radiationless processes in an isolated molecule. In addition, because the products are charged, a combination of mass spectrometric and photometric data yields information about photoionization reactions not now available for molecular fragmentation reactions. For example, the reaction cross sections for generation of specific charged products and the total photon absorption cross section may be measured and compared, thereby yielding the residual cross section corresponding to radiationless processes other than photoionization. From this information we can deduce some of the consequences of the competition between several radiationless processes in an isolated molecule. 

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],... 

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