Nitrogen dioxide, absorption spectrum

Fig. 2-16. Absorption spectrum and 0(3P) quantum yields for nitrogen dioxide. Absorption cross sections adapted from Bass el al. (1976), quantum yields from the authors listed. Threshold wavelengths for the formation of 0(3P) and O( D) are indicated.

A mixture of sulfur dioxide. S02. and sulfur vapor, at low pressure and with an electric discharge, forms sulfnr monoxide, SO Its presence is shown from its absorption spectrum, but upon separation it dispropor-tionates at once to sulfur and S02. Sulfur sesquioxide. S2Ojt, is formed by reaction of powdered sulfur with anhydrous SO3 S20 also dispropor-tionates (at 20°C in nitrogen) to sulfur and S02, Sulfur dioxide, S02, is... 

Hydro quinone transforms in the presence of irradiated nitrite to yield ben-zoquinone and hydroxybenzoquinone [78,79]. At the irradiation wavelength adopted in the cited works (365 nm), hydroquinone direct photolysis should be limited and benzoquinone most likely forms upon reaction between hydroquinone and hydroxyl (reactions 44 and 45 hydroquinone absorbs radiation at A, < 320 nm). Hydroxybenzoquinone is likely to be a product of benzoquinone photolysis. No nitration or nitrosation intermediates of hydroquinone were observed in the presence of nitrite under irradiation, differently from the cases of resorcinol and catechol [78,79]. The reaction between hydroquinone and nitrogen dioxide is, however, quite rapid [106,115], as confirmed by the marked inhibition of phenol nitration upon nitrite photolysis by added hydroquinone [62], The point is that the reaction between hydroquinone and NO2 mainly yields benzoquinone [62], Another interesting feature in the case of hydroquinone is the formation of the fairly stable semiquinone radical anion upon reaction between benzoquinone and depro-tonated hydroquinone. The spectrum of the resulting solution shows the typical absorption bands of the semiquinone at 308, 315, 403, and 430 nm [79]. 

They observed the same spectrum when nitrogen dioxide was used as the O atom source, indicating that 0( P) also reacted according to reaction (28). The absorption spectrum of NCO was also observed in both systems, and this species was explained by the reactions... 

Summary.—1. The absorption spectrum of nitrogen dioxide and nitrogen tetraoxide have been photographed at room temperature and the temperature of liquid air, respectively, and compared with previous work. 

In the visible region, the absorption by nitrogen dioxide can also contribute to the optical depth, especially in the lower stratosphere and troposphere. Moreover, molecular oxygen has two weak bands in the red region of the solar spectrum near 0.7 gm. 

The formation of oxygen atom 0( P) in the photolysis of nitrogen dioxide (NO2) is the fundamental reaction that causes direct production of O3 in the troposphere. In this section, absorption spectrum and 0( P) production quantum yields relevant to the tropospheric photochemistry are described. 

OP-UV spectrometry can be used to measure vapors or gases that have weak absorption characteristics, and therefore, low sensitivities in the IR spectrum. These include such compounds as nitrogen oxides, formaldehyde, ozone, sulfur dioxide, benzene, toluene, and xylenes, and also homonuclear diatomic molecules, such as chlorine. The compounds that can be determined by UV are much fewer (see Table 3.43) than those that are absorbing in the IR spectra. 

Nitrogen-to-iron weight ratios of 0.71 and 0.88 in 6 and 8, respectively, established the 71% and 88% oxidation ratios. The near-IR spectra of 12 and 13 had a broad absorption at 1000-2000 nm with maximum intensity at 1400-1700 nm. This band in BFD" (TCNQ)2 had previously been assigned to a photon-assisted intramolecular intervalence exchange (8, 9) and it confirmed that monooxidation of BFD units to [Fe(II)Fe(III)] occurred (BFD was dioxidized to its [Fe(III)Fe(III)] salts by Mueller-Westerhoff and Eilbracht (19) these salts had no absorption at 1400-1700 nm). Absorption at 600 nm was also pronounced. The Mossbauer spectrum of 12 was dominated by a single symmetrical absorption with a quadrupole splitting of 1.73 mm/sec which further confirms the BFD structure. Neutral BFD s doublet (2.40 mm/sec) was also observed. 

The absorption bands of water vapor and carbon dioxide are always present in the infrared spectrum of the expired breath because both these substances strongly absorb infrared radiation. On the other hand, oxygen, nitrogen, and the inert gases do not absorb infrared radiation and therefore cannot be detected— an advantage for the methods to be discussed. 

The adhesion of RFL-coated tire cords to rubber can be adversely affected if the dipped cords are exposed to ozone, UV light, nitrogen oxides, sulfur dioxide, or air before vulcanization into rubber. lyengar proposed that ozone exposure of RFL reduces adhesion because ozone attacks the double bonds of the butadiene component of the rubber latex and impairs its cocuring with the solid rubber compound. Infrared studies by Solomon reinforced this argument. When typical RFL films were exposed to ozone, the IR spectrum showed an increase in IR absorption at 1720 cm corresponding to an increase in the carbonyl content in the exposed film. An RFL film with no ozone exposure did not show this absorption at 1720 cm The increased carbonyl content is due to the reaction of some double bonds in the rubber with ozone and therefore, would leave fewer unsaturation sites for rubber crosslinking and adhesion. 

It is advisable to make reflection-absorption measurements at two or three different angles of incidence because the optimum angle of incidence varies with the type of substrate metal. As the reference material, the same metal as used for the substrate for the thin film is most appropriate. If this is not available, a stainless-steel plate or a plane mirror may be used but this may then cause some details of the measured sample spectrum to be obscured. It is very important to purge the inside of the spectrometer with dried air or nitrogen in order to remove water vapor and carbon dioxide as completely as possible, so that the measurements for the sample and reference material can be made under exactly the same conditions. 

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