Radical measurements

Packer, J.E., Willson, R.L., Hahnemann, D. and Asmus, K.-D. (1980). Electron transfer reactions of halogenated aliphatic peroxyl radicals measurements of absolute rate constants by pulse radiolysis. J. Chem. Soc. Perkins Transact. II, 296-299. 

TABLE 5.1. Ionization energies of organic radicals measured by using ZEKE spectroscopy. 

Rate Constants of Hydroperoxide Group Decomposition into Free Radicals Measured by Kinetics of Autoxidation and by Free Radical Acceptor Method... 

The literature data on the recombination of diphenylaminyl radicals correlate well (see Table 15.12). The rate constants of recombination of various aminyl radicals measured by flash photolysis vary from 105 to 109 L mol 1 s 1. For substituted diphenylaminyl radicals, a linear dependence was observed between log k9 and rr-Hammett [96] ... 

February) were selected as representative of the extremely clean conditions of the Southern Hemisphere Marine Boundary Layer. These very clean conditions (NO<3 ppt) correspond to the cleanest conditions under which radical measurements have been taken at ground level in the Southern Pacific Ocean. The two models agree to within 5-10% or less. 

Rate constants for spin trapping of alkyl radicals measured by the procedures outlined here, are collected with other spin-trapping rate data in Table 5. It will be seen that most nitrone and nitroso traps scavenge reactive radicals of diverse types with rate constants generally in the range 10s-10 1 mol-1 s l. Of the nitroso-compounds, the nitroso-aromatics (except for the very crowded TBN) are particularly reactive, whilst MBN and DMPO are the most reactive nitrones. Much of the data for spin trapping by nitrones has been accumulated by Janzen and his colleagues, who have discussed in a short review how steric and electronic factors influence these reactions (Janzen et ai, 1978). 

Vizzard, William J. Shots in the Dark. Lanham, Md. Rowman Littlefield, 2000. A former agent for the U.S. Bureau of Alcohol, Tobacco, and Firearms examines the back ound for gun control issues and surveys the key developments in gun control legislation starting with New York s Sullivan Law in 1911. Fie concludes with modest proposals for strengthening gun laws, believing that more radical measures would not be politically feasible. 

Figure 11.55 shows an altitude profile for peroxy radicals measured above the boundary layer over southern Germany using chemical amplification with the mass spectrometric derivatization measurement of OH (Reiner et ciL, 1998). Concentrations are again seen to be in the range of 10x-109 cm-3. 

Brauers, T., U. Aschmutat, U. Brandenburger, H.-P. Dorn, M. Hausmann, M. BeBling, A. Hofzumahaus, F. Holland, C. Plass-Dulmer, and D. H. Ehhalt, Intercomparison of Tropospheric OH Radical Measurements by Multiple Folded Long-Path Laser Absorption and Laser Induced Fluorescence, Geophys. Res. Lett., 23, 2545-2548 (1996). 

Eisele, F. L and J. D. Bradshaw, The Elusive Hydroxyl Radical. Measuring OH in the Atmosphere, Anal. Chem., 65, 927A-939A (1993). 

Reiner, T., M. Hanke, and F. Arnold, Atmospheric Peroxy Radical Measurements by Ion Molecule Reaction-Mass Spectrometry A Novel Analytical Method Using Amplifying Chemical Conversion to Sulfuric Acid, J. Geophys. Res., 102, 1311-1326 (1997). 

A second reason for the response of 03 to NOx at low VOC/NOx ratios is that at these high NOx concentrations, N02 competes with VOC for the OH radical by forming HN03 (reaction (13)). This terminates the chain oxidation of VOC and removes N02 from the system without forming 03. This chemistry has been confirmed by direct OH radical measurements thus, Eisele et al. (1997) report that OH concentrations increase with the NO concentration up to l-2 ppb but decrease thereafter due to the OH + N02 reaction. This is consistent with model calculations of isopleths of OH concentrations as a function of the VOC/NOx ratio, similar to the ozone isopleths in Fig. 16.14 (e.g., Kley, 1997) in the high NOx-low VOC... 

The syntheses of iron isonitrile complexes and the reactions of these complexes are reviewed. Nucleophilic reagents polymerize iron isonitrile complexes, displace the isonitrile ligand from the complex, or are alkylated by the complexes. Nitration, sulfonation, alkylation, and bromina-tion of the aromatic rings in a benzyl isonitrile complex are very rapid and the substituent is introduced mainly in the para position. The cyano group in cyanopentakis(benzyl isonitrile)-iron(ll) bromide exhibits a weak "trans" effect-With formaldehyde in sulfuric acid, benzyl isonitrile complexes yield polymeric compositions. One such composition contains an ethane linkage, suggesting dimerization of the transitory benzyl radicals. Measurements of the conductivities of benzyl isonitrile iron complexes indicate a wide range of A f (1.26 e.v.) and o-o (1023 ohm-1 cm.—1) but no definite relationship between the reactivities of these complexes and their conductivities. 

The ClO-BrO instrument was designed to test the theory that chlorine and bromine were the cause of the rapid loss of ozone over Antarctica. Its pedigree includes several versions of balloon-borne halogen radical measuring... 

Other molecules in the atmosphere oxidize NO to N02 aside from peroxy radicals, ozone being the most abundant. Therefore, a large background is present from the N02 produced because of the NO-ozone reaction as well as from ambient N02. This background must be periodically measured to ensure accurate determination of the peroxy radical signal. Typically, one-third to one-half of the time N2 is substituted for CO, and all those species that do not participate in the chain reaction are measured. Thus, the peroxy radical measurement is the difference between this background and the signal with CO present. 

Table I. Summary of Peroxy Radical Measurement Methods...

Several potential peroxy radical measurement techniques exist in the realm of atmospheric chemistry studies, although most have been used only in the laboratory. The techniques are summarized in Table I. Possibly, some laboratory methods could be applied to atmospheric measurements. The database for ambient peroxy radical concentrations in the troposphere and stratosphere is meager. Much of the available stratospheric data yield concentrations of H02 higher than those calculated with computer models. The reasons for this systematic difference are not known. In the troposphere, more measurements are called for in conjunction with other related species such as ozone, NO, NOjNo2 andjcv It wiH also t>e appropriate to develop multiple methods, and, when they have reached maturity, to perform intercomparison studies. 

Monks P.S., Zanis P Schuepbach E., and Penkett S.A. (1999) On photochemical control of ozone at Jungfraujoch (3,580 m asl) in spring based on peroxy radical measurements using FREETEX 96 and model results, Geoph. Res. Abstracts 1(3), 658. 

Figure 8. Concentration of different radicals measured from ESR spectra during copolymerization of vinyl acetate (VAc) with maleic acid (MA) ana of VAc with fumaric acid (FA) at different molar concentrations of MA in the VAc-MA system and FA in the VAc-FA system, respectively. (VAc-) and (MA-) refer to monomer radicals and (VAc-MA-) and (VAc-MA-) to the copolymer radicals observed. [VAc] = 5.5 X 10 2M ...

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