Atmospheric gases major constituents

Hydrocarbon molecules are abundant constituents of planetary atmospheres and major compounds in combustible gas mixtures and in fusion edge plasmas [7-11]. Methane is the simplest of these hydrocarbon molecules. Acetylene, C2H2, is the simplest hydrocarbon molecule that contains 2 carbon atoms. Thus absolute total and partial photon [24-27] and electron [15,28-34] ionization cross-sections and nascent fragment ion energy distributions [19,20,28,36-40] have been studied extensively for these molecules. For the deuterated methane molecule electron impact ionization and dissociative ionization cross-sections were determined for the CD (x=l—4) molecule and radicals applying a fast neutral beam technique [41]. Electron impact total ionization cross-sections have been determined also theoretically applying the BEB (Binary-Encounter-Bethe) model [42], the DM (Deutsch-Mark) method [43] and the JK (Jain-Khare) method [44], Partial electron impact ionization cross-sections were calculated for methane [45,46] as well as total electron impact cross-sections for various CH radicals [47]. The dissocia-... 

Other gases are found on the surface of the earth and in the atmosphere. Methane (CH4), formerly known as marsh gas, is produced by bacterial processes, especially in swampy areas. It is a major constituent of natural-gas deposits formed over many millennia by decay of plant matter beneath the surface of the earth. Recovery of methane from municipal landfills for use as a fuel is now a commercially feasible process. Gases also form when liquids evaporate. The most familiar example is water vapor in the air from the evaporation of liquid water it provides the humidity of air. 

Carbon is a major constituent of most of our fuels— natural gas, petroleum, coal, wood, and other biomass. When burned for their heat content, these fuels produce carbon dioxide, which escapes into the atmosphere. In the carbon cycle, this carbon dioxide is trapped by plants and reincorporated into useful substances such as cellulose and starch via photosynthe-... 

Noble gases are intrinsically difficult to detect by spectroscopy. For example, solar photospheric spectra, which form the basis for solar abundance values of most elements, do not contain lines from noble gases (except for He, but this line cannot be used for abundance determinations). Yet, ultraviolet spectroscopy is the only or the major source of information on noble gas abundances in the atmospheres of Mercury and comets. In the Extreme Ultraviolet (EUV), photon energies exceed bond energies of molecules and the first ionization potential of all elements except F, He, and Ne, so that only these elements are visible in this part of the spectrum (Krasnopolsky et al. 1997). Other techniques can be used to determine the abundance of He where this element is a major constituent. Studies of solar oscillations (helioseismology) allow a precise determination of the He abundance in the solar interior, and the interferometer on the Galileo probe yielded a precise value for the refractive index and hence the He abundance in the upper atmosphere of Jupiter (see respective sections of this chapter). 

Hydrogen is the most abundant element in the universe, being the major constituent of all stars. Most of the hydrogen found on earth is in the combined state—in compounds with other elements. The amount of elemental hydrogen (H2) found on earth is actually very small. The atmosphere contains only 0.00005% H2 gas. Therefore, when H2 gas is required to produce a substance such as NH3 in the reaction... 

Natural gas, often found associated with petroleum deposits, consists mainly of methane (about 80%) and ethane (5% to 10%), with lesser amounts of some higher alkanes. Propane is the major constituent of liquefied petroleum gas (LPG), a domestic fuel used mainly in rural areas and mobile homes. Butane is the gas of choice in some areas. Natural gas is becoming an energy source that can compete with and possibly surpass oil. In the United States, there are about a million miles of natural gas pipelines distributing this energy source to all parts of the country. Natural gas is also distributed worldwide via huge tankers. To conserve space, the gas is liquefied ( — 160°C), because 1 cubic meter (m ) of liquefied gas is equivalent to about 600 m of gas at atmospheric pressure. Large tankers can carry more than 100,000 m of liquefied gas. 

As the major constituent of the atmosphere (79%), dinitrogen (N2) ubiquitous on earth and as a generally inert gas frequently used as protecting gas against contamination with undesired dioxygen and moisture in many applications and organometaUic synthesis. Several factors contribute to its lack of reactivity The N=N bond is the second strongest chemical bond... 

THE LIGHT STABLE isotopes of hydrogen, carbon, nitrogen, oxygen, and sulfur (HCNOS) are natural tracers of geologic/planetary processes. These elements and their isotopes are major constituents of common compounds that are foimd in gas, liquid, and solid form. As such, they make excellent tracers of interactions between major reservoirs such as the atmosphere, hydrosphere, lithosphere, and asthenosphere of a planetary bo(. Their isotopic ratios are readily measured by mass spectrometric methods. 

There are two interesting molecules that are derived from carbon and oxygen alone. Earlier, we encountered carbon dioxide, CO2, as a constituent of our atmosphere, a product of the combustion of fossil fuels, and a major contributor to global warming. An even simpler molecule is carbon monoxide, CO, a toxic gas and a minor product of incomplete combustion of fossil fuels. 

Alkanes are often found in natural systems. They are the main constituents in the atmospheres of the planets Jupiter, Saturn, Uranus, and Neptune. Methane is also thought to have been a major component of the atmosphere of the early Earth. Natural gas and oil are primarily made of alkanes. 

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