Methane absorbance

Alkane groups unsubstituted by heteroatoms absorb downfield from TMS to about 60 ppm. (Methane absorbs at 2.5 ppm upfield from TMS.) Within this range we can predict the chemical shifts of individual C atoms in a straight chain or branched chain hydrocarbon from the data in Table 4.1 and the formula S = -2.5 + SnA. 

Methane is the most abundant hydrocarbon in the atmosphere. It plays important roles in atmospheric chemistry and the radiative balance of the Earth. Stratospheric oxidation of CH4 provides a means of introducing water vapor above the tropopause. Methane reacts with atomic chlorine in the stratosphere, forming HCl, a reservoir species for chlorine. Some 90% of the CH4 entering the atmosphere is oxidized through reactions initiated by the OH radical. These reactions are discussed in more detail by Wofsy (1976) and Cicerone and Oremland (1988), and are important in controlling the oxidation state of the atmosphere. Methane absorbs infrared radiation in the troposphere, as do CO2 and H2O, and is an important greenhouse gas (Lacis et al., 1981 Ramanathan et al., 1985). 

After water vapor and C02, methane (CH4) is the third most important greenhouse gas. Each additional molecule of CH4 added to the atmosphere absorbs about 20 times as much long-wave infrared radiation as does a molecule of carbon dioxide. This occurs in part because some of the absorption spectrum of methane lies in windows in the carbon dioxide absorption spectrum (see Fig. 4-42) therefore, methane absorbs wavelengths that are not already being highly attenuated by carbon dioxide. Currently, the global concentration of methane in the atmosphere is approximately 1.7 ppm and is increasing at an annual rate of approximately 0.01 ppm per year (Table 4-14). The seasonal fluctuations shown in Fig. 4-44 may correspond to seasonal... 

J.Z. Larese (1998). Physica B, 248, 297-303. Neutron scattering studies of the structure and dynamics of methane absorbed on MgO(lOO) surfaces. 

Methane and carbon dioxide produced in soils are transported into the atmosphere by diffusion and mass flow via two pathways (1) the aerenchyma tissues of plant roots and stems and (2) flux from soil to the overlying water column (Figure 5.61). Gas exchange in plants is discussed in detail in Chapter 7. Carbon dioxide is highly soluble and undergoes various chemical reactions, and it may be difficult to estimate flux accurately without considering aU associated reactions. Because of the potency (on molecule-to-molecule basis, methane absorbs 25 times as much infrared radiation as carbon dioxide) of methane as greenhouse gas, we will focus our discussion on methane emissions from wetlands. 

The alternative electromagnetic field is exerted on coal particles in the last three steps with fixed parameters which are voltage of 500 to 1200 V, and frequency of 0.54 to 1.58 MHz. When alternative electromagnetic field is exerted in the second step or the third step, it is exerted all the time. When it is applied in adsorptive experiment, the operation are as following First, the coal samples is pumped to vacuum, then let one atmosphere methane absorb into coal samples until it reach to adsorptive balance, meanwhile record adsorptive amount changing with time. When the measurement of high... 

Fig. 8. Experimental and calculated xenon loadings for xenon and methane absorbed on to NaA zeolite. Occupancies for the different loadings in Xe/alpha cage are shown. (Courtesy of Cynthia Jameson. Reprinted from ref. 173 with permission. Copyright 2000, American Institute of Physics.)...

A solvent-free synthesis of flavones which involves the MWI of o-hydroxydibenzoyl methanes absorbed on montmorillonite KIO clay for 1 to 1.5 min has been achieved. Rapid and exclusive formation of cyclized flavones occurs in good yields (Scheme 15) ... 

Figure 16. Correlation of Cl 2pj/2 binding energy with -A//ab for trichloro-methane absorbed in a series of polymers. (From Ref. 120.) Key to data points + aromatic moi.sture cured urethane poly(vinyl acetate) A poly(methyl-methaciylate) T poly(ethylene oxide) poly( -butylmethacrylate poly(cy-clohexyl methacrylate).

S.N. Bagayev, E.V. Baklanov, E. Titov, V.P. Chebotayev Reproducibility of the frequency of an He-Ne-laser with a methane absorbing cell. JETP Lett. 20, 130 (1974)... 

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