Measurement methods hydroperoxyl radical

Measurements of tropospheric HO and H02 concentrations have been accomplished by both direct and indirect means. Direct techniques are based on the measurement of the hydroxyl or hydroperoxyl radical using some physical property of the radicals themselves e.g. optical absorption. Indirect techniques refer to methods based on the measurement of compounds that are uniquely and/or quantitatively formed from or destroyed by HO or HO2. Examples of these techniques for both [HO ] and [HO2 ] will be given. 

The interatomic distances in peroxyl radicals were calculated by quantum-chemical methods. The experimental measurements were performed only for the hydroperoxyl radical and the calculated values were close to the experimental measurements (see Table 2.5). The length of the O—O bond in the peroxyl radical lies between that in the dioxygen molecule (r0—o= 1.20 x 10-10m) and in hydrogen peroxide (r0—o= 1-45 x 10-lom). 

Far-infrared absorption spectra of H02 in the gas phase have been detected with a water-vapour laser magnetic resonance spectrometer.40 The identification of H02 as the absorbing species is based on a partial analysis of the spectra, and on a variety of different chemical methods used to produce the radical. Using the photochemical 1802 competitive isotopelabelling technique, rate constants have been determined for the reaction of the hydroperoxyl radical with atmospheric sulphur dioxide.41 All measurements were made relative to the disproportionation reaction ... 

The high selectivity of hydroperoxyl and alkylhydroxyperoxyl radicals toward quinone has been used for the development of an original method for measuring the rate constant of peroxyl radicals with alcohols (see Chapter 7). 

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