Absorption, spectra gases

This characteristic is used to analyze aromatics in gas oil cuts an example of a UV absorption spectrum is shown in Figure 3.5. 

The above figure shows part of the infrared absorption spectrum of HCN gas. The molecule has a CH stretching vibration, a bending vibration, and a CN stretching vibration. 

When evaluating gas concentrations in practical applications, a reterence spectrum is least squares fitted to the received absorption spectrum. This im proves the system accuracy, since the spectral fingerprint over the whole scanning range contributes to the result.- ... 

Raman spectra of S2 in its triplet ground state have been recorded both in sulfur vapor and after matrix isolation using various noble gases. The stretching mode was observed at 715 cm in the gas phase [46], and at 716 cm in an argon matrix [71]. From UV absorption and fluorescence spectra of sulfur vapor the harmonic fundamental mode of the S2 ground state was derived as t e = 726 cm . The value corrected for anharmonicity is 720 cm [26, 27]. Earlier reports on the infrared absorption spectrum of 2 in matrix isolated sulfur vapor [72] are in error the observed bands at 660, 668 and 680 cm are due to S4 [17] and other species [73]. 

Flash photolysis of either H2S [66] or H2S2 [67, 68] in the gas phase at low partial pressures produces, inter aha, HS2- radicals which were detected by their UV absorption spectrum in the 307-380 nm region. In addition, singlet and triplet 2 molecules as well as SH radicals are formed from H2S2, and the following reaction mechanism has been proposed (photolysis in the region 200-300 nm in the presence of excess CO2) [67] ... 

Schematic representation of an apparatus that measures the absorption spectrum of a gaseous element. The gas in the tube absorbs light at specific wavelengths, called lines, so the intensity of transmitted light is low at these particular wavelengths.

The following physico-chemical properties of the analyte(s) are important in method development considerations vapor pressure, ultraviolet (UV) absorption spectrum, solubility in water and in solvents, dissociation constant(s), n-octanol/water partition coefficient, stability vs hydrolysis and possible thermal, photo- or chemical degradation. These valuable data enable the analytical chemist to develop the most promising analytical approach, drawing from the literature and from his or her experience with related analytical problems, as exemplified below. Gas chromatography (GC) methods, for example, require a measurable vapor pressure and a certain thermal stability as the analytes move as vaporized molecules within the mobile phase. On the other hand, compounds that have a high vapor pressure will require careful extract concentration by evaporation of volatile solvents. 

In applying RAIRS to CO adsorption, the contribution from CO molecules in the gas phase to the absorption spectrum at CO pressures above 10-3 mbar completely obscures the weak absorption signal of surface adsorbed CO. Beitel et al. found it possible to subtract out the gas phase absorption by coding the surface absorption signal by means of the polarization modulation (PM) technique applied to a conventional RAIRS spectrometer, p-polarised light produces a net surface electric field which can interact with adsorbed molecules, whereas both polarization states are equally sensitive to gas phase absorption because gas phase molecules are randomly oriented. By electronic filtering a differential spectrum is computed which does not show contributions from the gas phase and which has much higher surface sensitivity than a conventional RAIRS setup. 

Photolysis in the gas phase leads to the quantitative production of nitrogen and methyl radicals. Photolysis in solution, however, results in a shift in the absorption spectrum to longer wavelengths due to the production of a new species, which is identified as the cw-azomethane (the trcms configuration is the normal isomer). Similarly, irradiation of tro/u-azoisopropane<3) results in trans-cis isomerization to the cis isomer ... 

Figure 4. The transient absorption spectrum of Cr(C0)5 0.5 msec following a) XeF, b) KrF and c) ArF photolysis of gas phase Cr(C0)6. The arrows in a) indicate the Cr(C0)5 absorptions. (Reproduced with permission from reference 9. Copyright 1986 American Chemical Society.)...

Fig. 14. Infrared absorption spectrum of anode films prepared at Ts = 25°C with boron fractions xg = 0 (top), 0.25, 0.5 0.75, and 1 (bottom), respectively, in the gas. The film thickness and the transmission measured at v = 4000 cm-1 are given for each curve. From C.C. Tsai (1979).

CF2 is unique among carbenes because of its high stability and low reactivity. Investigations of the ultraviolet absorption spectrum of CF2 have led to estimates of roughly 10 milliseconds to one minute for the half-life of CF2 at pressures in the region of one atmosphere. The gas phase molecule does not react with BF3, N20, S02, CS2 or CF3I at 120 °C5 K The nature of CF2 is perhaps best presented in separate sections discussing its preparation, structure and physical properties, reaction chemistry, and reaction kinetics. 

The infrared spectrum of GeF2 has also been reported 10 3 It was necessary to study the matrix-isolated spectrum for two reasons. First, the examination of the ultraviolet absorption spectrum of GeF2 indicated that at least ten of the bending states were populated, and second, germanium has five abundant isotopes. These suggested that the gas phase spectrum would be broad and ill de-... 

FlO. 4. Vacuum-ultra violet absorption spectrum of oxygen gas. The positions at which Rydberg series convergence limits occur are marked X—X. (We are indebted to Professor W. C. Price for this photograph.)... 

One of the first applications of this chopped-beam irradiation technitriplet spectra was reported by Labhart From a knowledge of the intensity of the irradiation light, he determined the quantum yield of triplet generation to be 0.55 0.11 for outgassed solutions of 1,2-benzanthrazene in hexane at room temperature. Hunziker 32) has applied this method to the study of the gas-phase absorption spectrum of triplet naphthalene. A gas mixture of 500 torr Na, 0.3 mtorr Hg, and about 10 mtorr naphthalene was irradiated by a modulated low-pressure mercury lamp. The mercury vapor in the cell efficiently absorbed the line spectrum of the lamp and acted as a photosensitizer. The triplet state of naphthalene was formed directly through collisional deactivation of the excited mercury atoms. 

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