Disappearance cross section

A quantity related to the disappearance yield for a particle of a species which covers a solid surface with a surface density 9 (A), is the disappearance cross-section, ctd (A) ... 

Recently, the CH4+-CH4 reaction has been investigated (9) by measuring the CH4 + disappearance cross-section rather than CH5 + formation cross-sections. Results of this work are shown in Figure 9. Two mechanisms cause a loss of CH4 + ions from the total ion yield in the methane mass spectrum. There are loss processes in the ion source which generate new ions, CH5 +, and possibly other products. Other loss... 

Figure 10. Comparison of the velocity dependence of the disappearance cross-section of CHa+, formation cross-section of CH0 +, and Langevin orbiting collision cross-section, all as a function of reciprocal average kinetic energy of ions in the mass spectrometer source...

Giardini-Guidoni and Friedman [155] carefully reinvestigated the reaction in 1966, paying special attention to the energy transfer problem. Firstly, they measured the disappearance cross-sections of CH4 and found that they vary linearly with in excellent agreement with the... 

Indeed, the sum of the cross-sections for CH5 and CH3 formation agreed well with the disappearance cross-section of CH4 (and accordingly with the G—S theoretical cross-section) at all energies studied. By changing the energy of the ionizing electrons systematically, it was found that CH3 is also formed by the initial internal excitation of CH4. 

Reactions of all the fragment ions produced by impact of 70—100 eV electrons have also been studied extensively [134, 277, 284—289]. According to Abramson and Futrell [284] who used a tandem mass spectrometer, many of the smaller fragment ions from propene are very reactive towards propene and, in fact, a total of 44 secondary ions have been detected with 100 eV electrons. MacKenzie Peers and Vigny [287, 288] have determined the disappearance cross-sections for the parent and all of the fragment ions. Results for some of these ions are given in Table... 

Disappearance cross-sections of parent and some fragment ions in propene [288]... 

Disappearance cross-section estimated by MacKenzie Peers from the formation cross-section for C4HS of Abramson and Futrell. 

Reactions of some of the Cj-fragments, as well as the disappearance cross-sections for all of the fragments (C, to C3) have also been studied [277, 284, 286]. However, we will not discuss all of them here but simply mention that the formation of C4H2 and C5H3 from CjH [286] and the formation of CsH from CjHj [134, 277] have two of the largest cross-sections among all reactions in propene. 

The SIMS process, as it relates to polymers, is characterized by three important parameters ion yield, transformation probability, and disappearance cross section. The ion yield (Y) is the ratio of the number of secondary ions produced divided by the number of primary ions incident on the sample Y = N(si)/N(pi). SIMS bombardment of a surface covered by a monolayer or less results in an exponential decay of the measured signal intensity 1(f) = I° exp[-(7(x)ypf/e] where is the primary ion current density, X the species measured, and cthe disappearance cross section. Thus <7 can be calculated from SIMS intensity decay curves. The disappearance cross section is the damage area caused by the primary ion which leads to desorption of a polymer molecule. 

Disappearance cross section A parameter used in Static SIMS for describing the disappearance of a useful signal during sputtering... 

Disappearance cross section (T Defined as the area from which surface species have disappeared under PI bombardment, irrespective of their fate the magnitude of a depends on the species fragment analyzed (i.e.. O = 0(M)). Typical values are around cm- (see Section 1.4.2). 

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