Hydrogen abundance, estimation

At lower column densities, one is looking at systems where only a small fraction of the hydrogen is neutral metal lines (e.g. C il-iv, Si Il-iv) are weak and quantitative abundance estimates require an understanding of the ionizing radiation field, which may involve uncertainties of a factor of 3 or more the O VI doublet at AA 1032,1037 A, an important diagnostic, suffers from obscuration by the Ly-a forest. Existing results show a correlation with column density, with < [O/H] > — 1.5 for JV(H I) > 1015 cm-2 and-----2.5 for 10145 < /V(H I) < 1015 cm-2, perhaps reflect-... 

Figure 13. The diagonal band is the SBBN-predicted helium-4 mass fraction versus the SBBN-predicted deuterium abundance (by number relative to hydrogen). The width of the band accounts for the theoretical uncertainties in the SBBN predictions. Also shown by the filled circle and error bars are the primordial 4He and D abundance estimates adopted here.

Bodner and Domin (2000) demonstrated the inability of many university students to interpret abbreviated structural portrayals with some atoms implied, rather than shown. The students were asked to predict the major products of the reaction of bromine with methylcyclopentane portrayed as in Fig. 1.2, and to estimate the ratio of the products if bromine radicals were just as likely to attack one hydrogen atom as another. Most of the 200 students predicted three products, with a relative abundance 3 2 2 (Fig. 1.4). 

The hydrogen was examined spectrographically as described by Urey, Brickwedde and Murphy. No quantitative estimate of the abundance of can be made by this method, but the photographs show that there is a very definite increase in the abtmdance of relative to in these residual solutions. 

Herzberg was able to point out another line at 816.6 nm which he identified as a double transition, partially overlapped by an adjacent CH4 band in the Uranus spectra. In the laboratory spectra recorded with unmixed hydrogen, this double transition was relatively strong, but in the photographic plates of Uranus the feature was much weaker relative to the S3(0) line. This observation led Herzberg to conclude that sizeable He concentrations exist in these atmospheres (albeit the estimates of [He] [H2] abundance ratio seem high), because the S3(0) feature is enhanced by the presence of He, but H2-He pairs cannot undergo double transitions these features thus appear weak in Kuiper s plates relative to the S3(0) feature. 

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