Absorption spectrum hydroxyl radical

Four IR absorption bands have been identified in the spectrum of the hydroxysulfonyl radical (HOSO 2) which has been obtained by the reaction of hydroxyl radicals with sulfur dioxide in argon matrix at 11 K16. The observed bands at 3539.9 and 759.5 cm 1 have been assigned to O—H and S—OH stretching modes while the bands at 1309.2 and 1097.3 cm-1 have been assigned to the asymmetric and symmetric stretching modes of the double bonded S02 moiety. These data are consistent with the theoretical prediction on the geometry of the hydroxysulfonyl radical12. 

In a pulse radiolysis study of solutions of CdS of different particle size, the rate of reaction of the OH radical with the colloidal particles was studied as well as the absorption spectrum of the products The hydroxyl radical reacts on its first encounter... 

The central role of hydroxyl radicals in atmospheric chemistry is well illustrated by examining the atmospheric cycles of methane and carbon monoxide. A quantitative assessment of both of these species was carried out in the 1920s in Belgium by Marcell Migeotte, who detected their absorption lines in the spectrum of infrared solar radiation reaching Earth s surface. 

The molecular ion of water is shown in parenthesis because it rapidly converts to OH and H30+. The solvated electron (2), corresponding to an electron bound to several water molecules in a fluid system, is designated here as eaq , but will also be denoted as es" for an electron bound in other polar media. It is highly mobile, has a broad, intense absorption spectrum with a maximum at 720 nm, and is a powerful reductant. The hydroxyl radical, OH, is also very mobile and is a strong oxidant it exhibits a weak absorption in the 240 nm region. The hydrogen atom, H , is a reductant and exhibits only a weak absorption in the ultraviolet... 

The very simple ultraviolet absorption spectrum of PAN, first observed by Stephens for samples obtained from ethyl nitrate photolysis with gas chromatographic separation, was confirmed in the early 1980s by using high purity samples.Interestingly, PAN has no strong structural features in its ultraviolet spectrum and does not absorb above 290 nm. The PAN molecule is not readily photolyzed in the atmosphere at altitudes below 5 to 7 km. " Photolytic lifetimes for PAN are calculated to be on the order of 20 X 10 sec The reaction of PAN with hydroxyl radical... 

The existence of the hydroxyl radical as a separate. If transient, entity was first recognized in 1924 by Watson (19), who proposed that the water vapor bands emitted by flames and electric discharges In moist air were due to the OH radical, and not to excited H2O. In 1928 Bonhoeffer and Relchardt (20) obtained the absorption spectrum of the OH radical in partially dissociated water vapor at v>1873°K, and In 1935 Oldenberg (21) was able to follow the decay of the radical In the products flowing from an electric discharge through water vapor. This latter work was of Importance since the OH radical could then be monitored In a system applicable to kinetic studies. Early combustion studies showed that the hydroxyl radical Is also an Important constituent of flames, the most prominent feature of flame spectra (22) being emission from the (a2i + - X Il) band system of the OH radical. 

The last reaction is an important source of OH radicals in the troposphere. Hydroxyl radicals do not undergo reactions with any of the major constituents of air, but they react rapidly with many trace compounds and represent the most significant oxidant in the troposphere. Up to 25% of the 0( D) atoms are converted to OH under favorable atmospheric conditions. The spectral window available for the production of 0( D) and OH radicals is quite narrow. Toward short wavelengths, it is limited by the cut-off of the solar spectrum near 300 nm at wavelengths near 320 nm, it becomes ineffective by the diminishing quantum yield for 0( D) formation in the photolysis of ozone. Figure 1 illustrates the overlap between solar radiation intensity, the O3 absorption spectrum, and the 0( D) quantum yield. The area underneath the action curve shown at the bottom of the figure represents the photodissociation coefficient... 

The reaction of OH with [(NH3)6Co py] produces a reactive transient with a second-order rate constant of 6.5 x 10 1 mol- s- (pH = 5.2). The absorption spectrum of this transient has a maximum at 320 nm (e = 18001 mol cm ) and is similar to the spectrum obtained in the radiolysis of free pyridine. It is proposed that the hydroxyl radical adds to the pyridine ligand to form a ligand radical co-ordinated to the Co centre. This species undergoes intramolecular redox to yield Co and pyOH with a rate constant of 6.0 s. ... 

The first step in the reaction of [Co(NH3)5(py)] with hydroxyl radicals is proposed to be attack at the coordinated pyridine. The absorption spectrum of the [Co(NH3)5(pyOH)] radical complex thus produced is given. This intermediate then undergoes redox decomposition. The intermediacy of such a radical complex in the present system is supported by earlier suggestions of the existence of the species [Co(NH3)5(O2C0] and of this or related species during permanganate oxidation of the formate complex [Co(NH3)5(02CH)]. ... 

Recently in the literature, Forbes et al. [42] have proposed an alternative mechanism for the observed polarisation phase. They note that in the EPR spectrum there is a small net absorptive peak (E/A ) which can arise when the two radicals have different g-factors. In the reaction scheme investigated by Das and co-workers [1], no net absorptive peak is seen since the hydroxyl radicals are rapidly scavenged to... 

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]. 

From the seeds of Castilleja rhexifolia deoxyrhexifoline (24) was isolated (35). The molecular ion was observed at m/z 191, 16 amu less than 23, and the difference of one oxygen atom was confirmed by high-resolution measurement. The base peak was observed at m/z 176 due to loss of a methyl radical. No hydroxyl absorption was seen in the IR spectrum, and the NMR spectrum showed no downfield oxymethine proton. Rather, two sets of methylene protons (3.38,3.13 ppm 2.38,1.67 ppm) were seen. Thus, the alkaloid was deduced to be the 5-deoxy derivative and was named deoxyrhexifoline (24) (35). The relationship between methyl boschniaki-nate and deoxyrhexifoline has not been established, but the available data would appear to indicate that they are the same alkaloid. Neither group reported an [a]D for the respective isolates. 

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