Reactions of Atoms and Free Radicals

Details of studies of the kinetics and dynamics of elementary reactions involving atomic species are provided in Table 12. Although many of these deal only with kinetics or dynamics and appear to have little connection with photoprocesses , it will be found that such studies have made use of radiation in some way-to initiate a reaction or to probe a product state distribution, 

Weulerese, J. Chim. Phys. Phys.-Chim. Biol., 1983, 80, 331. 

The photolysis of HBr at 193 nm has been used by Kleinermanns and Wolfrum as a source of translationally hot H atoms in a series of investigations of the elementary reactions of H with O2, H2O, and C02. They have provided a summary of these studies which also includes other laser-induced processes. Nascent vibrational, rotational, and fine-structure state distributions of OH(X n) resulting from the H( S) + 02( Sg ) reaction were presented simultaneously with the results of classical trajectory calculations of the total and state-to-state cross-sections for this reaction performed on an ab initio potential surface. OH vibrational and rotational excitation was found to be high and a preference for the tt component of the A-doublets was noted. The latter was taken to indicate that the reaction takes place in a planar configuration at high collision energies. For H+H2O and H+CO2, similar 

Breckenridge and Umemoto measured the nascent rotational state distributions of MgH(t) = 0,1) and MgD(u = 0) produced in the reactions between Mg( Pi) and H2/D2. They observed bimodal distributions, with the major components (ca. 90% of the total) showing very high rotational excitation and the minor components lower rotational excitation. The reactions producing highly rotationally excited MgH(MgD) were suggested to involve side-on insertion of the Mg( Pi) into H2(D2), consistent with at initio studies of MgHa potential surfaces. The minor components were discussed in terms of less efficient end-on insertion, but other possible explanations were also considered. 

An optical parametric oscillator (OPO) was used to select HF(n = 1) in each of the rotational states J = 0—7 in a study of the effect of rotational excitation on the product state distributions in the reaction  

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A number of chemiluminescent reactions have been studied by producing key reactants through pulsed electric discharge, by microwave dissociation, or by observing the reactions of atoms and free radicals produced in the inner cone of a laminar flame as they diffuse into the flame s cool outer cone (182,183). These are either combination reactions or atom-transfer reactions involving transfer of chlorine (184) or oxygen atoms (181,185—187), the latter giving excited oxides. 

Reaction of atoms and free radicals (see references cited in Jonah et al. [9]). 

Nuclear tunneling has been most explicitly demonstrated in low-temperature reactions of atoms and free radicals in solids. The common feature of these reactions is the use of radiation to obtain unstable species which undergo reaction. As a rule, the active particles were recorded with the help of the EPR spectroscopy. A wide class of reactions has been studied... 

Kharasch, M. S., J. Kuderna, and W. Nudenberg Reactions of Atoms and Free Radicals in Solution. XXXIII. Photochemical and Peroxide-induced Addition of Cyclohexanone to 1-Octene. J. org. Chem. 18, 1225 (1953). 

The theoretical models discussed above are frequently employed in the description of the kinetics of gas-phase reactions, especially reactions of atoms and free radicals. This class of reactions is of interest in a broader scientific context, and a better understanding of their mechanism is of primary importance for the development of chemical modeling. Free atoms and radicals are very reactive species, which occur in and take part in many different reaction systems. Therefore, a radical reaction usually proceeds in competition with a few parallel or subsequent processes. The kinetic behavior of the reaction system may be very complicated and difficult for quantitative description. Theoretical investigations of the reaction kinetics provide information useful for a better understanding and correct interpretation of experimental findings. Results of ab initio calculations are employed to evaluate the rate constant in terms of the computational methods of the reaction rate theory. 

Kharasch MS, Jensen EV, Urri WH (1947) Reactions of atoms and free radicals in solution. X. The addition of polyhalomethanes to olefins. J Am Chem Soc 69 1100-1105... 

Reactions of Atoms and Free Radicals Studied in Discharge-Flow Systems... 

REACTIONS OF ATOMS AND FREE RADICALS 4.2.7. Absolute and Relative Concentrations... 

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