Fractional abundance

Instead of the fractionation factor (apQ) for two substances (P,Q), a slightly different fractional abundance (/pq) may be defined ... 

Figure 4. Variations with pressure of the fractional abundances of the species in the principal chain of ion-molecule reactions in ethylene...

The mass contributed by each isotope is proportional to its fractional abundance, as given by Equation ... 

Elemental molar mass = (Fractional abundance) (Isotopic molar mass)... 

The molar mass of a naturally occurring mixture of isotopes is the weighted average of the isotopic molar masses. Each isotope contributes to the total in proportion to its percentage (fractional) abundance, and the average is calculated using Equation. ... 

First, the percentages must be converted to fractions by dividing by 100%. Then we multiply these fractional abundances by the Isotopic masses and add the results. A table helps in organizing these manipulations ... 

A fifth success concerns carbon monoxide, the dominant interstellar molecule from an observer s point of view. Despite all the uncertainties and problems with the model calculations, which will be amply brought out in this review, the predicted fractional abundance of CO is large and in the range of 10"5 to 10-4, in excellent agreement with observation. 

Perhaps the source with the largest fractional abundances of unsaturated complex molecules is the small condensation in the Taurus complex known as TMC-1 (Taurus Molecular Cloud -1) which, although it shows evidence for substructure, can be considered to have average physical conditions (n = 104 cm-3 and T = 10 K). Table 2 contains a comparison of observed4 abundances in TMC-1 for almost 50... 

Table 2. Observed Fractional Abundances in TMC-1 (in Relation to H2 Abundance) Compared with Calculated Values (n = 1 x 104 cm 3 = n(H2) T = 10 K) at a Time of 105 Years...

It is possible that electrons are not the major carrier of negative charge in dense interstellar clouds. It has been suggested that if a large fractional abundance of polycyclic aromatic hydrocarbons (PAHs) exists throughout dense interstellar clouds (see Section I), then electron sticking reactions of the type,... 

Element Isotope Fractional abundance 1 %o change International standard... 

If no KIE is present, the contribution of the derivative atom to the measured 8 value of the derivatised compound can be calculated using a simple mass balance equation (14.2), where n is number of moles of the isotope of interest, F is the fractional abundance of the isotope of interest, c refers to the compound of interest, d refers to the derivative group and... 

Each of the isotopic masses is multiplied by its fractional abundance. The resulting products are summed to obtain the average atomic mass. 

Each of the three percents given is converted to a fractional abundance by dividing it by 100. 

Then the expression for the weighted-average atomic mass is used, with the percent abundances converted to fractional abundances by dividing by 100. The average atomic mass of potassium is 39.0983 u. 

Table 6.1. Fractional abundance of elements relative to hydrogen...

Mo+ and Mc>2+ one may resort to a multinomial expansion coefficient analysis. Let us represent the fractional abundances of the 7 Mo isotopes by a, b, c, d, e, f and g. The calculated and experimental fractional abundances of the 15 mass lines in Mo + are listed in Table 2.4. When the calculated abundances are compared with the experimental abundances, one reaches the conclusion that the spectrum shown in Fig. 2.17 contains few if any Mo+ ions. If on the other hand, a fraction of the ions are Mo+, say p, then the relative abundances of each mass line can also be calculated. For example, that of Min = 92 should be [pa + (1 — p)a2], and that of M/n = 94 should be [pb + (1 — p)(b2 + 2ad), etc. Thus the fraction p can be obtained by best fit of theoretical abundances and experimental abundances of different Min mass lines. 

The fractional abundances for A- and B-type atoms, atom-probe signals, are given by as registered in the... 

This statistical analysis can be easily extended to a multiple-component system. For an /V-component system with fraction abundances/ ,, . . ., /v, one has... 

Increased ion-source pressures and/or introduction of paramagnetic molecules, such as NO, cause deactivating collisions that convert excited ions into ground-state species13 61,63,64-66 (see Table I). The fractional abundance of excited states in an ion beam may thus be lowered without a concomitant reduction in total ion intensity, which would occur if the ionizing electron energy were simply lowered. 

The fractional abundances of excited states in ion beams have been determined by making use of their different reactivity characteristics. Three methods have been employed, and these are described using 0+ ions as an example. 

If a given ion-neutral reaction is known to occur only for ground-state ions, it is quite straightforward to determine the fractional abundance of the excited state. For instance, the reaction 0+(N2,N)NO+ proceeds with 0+(4S) reactant ions but not with ions in the 2D state.4b,c The cross section for this reaction has been determined as a function of the ionizing electron energy used to produce the 0+. The observed cross section at any given electron energy can be written as a sum of the contributions of the two... 

SOURCE GAS ELECTRON ENERGY (eV) APPROXIMATE FRACTIONAL ABUNDANCE REACTIONS STUDIED REMARKS REFERENCES... 

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