Earlier experimental results on the kinetics of relaxation to equilibrium in R + O 2 a RO 2 reactions (R ) CH 3 , C 2 H 5 , i-C 3 H 7 , t-C 4 H 9 , CH 2 Cl, CHCl 2 , and CCl 3 ) are reanalyzed using an improved kinetic mechanism which accounts for further reactions of the RO 2 adduct. Reaction enthalpy ∆H°2 98 (R + O 2 a RO 2 ) values are obtained from the third-law treatment of the temperature dependencies of the equilibrium constants K P (T) resulting from the reinterpretation of the original kinetic data. The R-O 2 bond strengths for alkyl and chloroalkyl radicals (R ) ‚C(CH 3 ) i Cl j H k , i + j + k ) 3) can be represented by a linear function of the numbers of C-C (N C-C ) and C-Cl (N C-Cl ) bonds at the C atom forming the C-O bond:). The values of ∆H°2 98 (R + O 2 a RO 2 ) are used to calculate the enthalpies of formation for the RO 2 peroxy radicals and ROOH hydroperoxides.

Electronic mail: dlosbor@sandia.gov (DLO), cataatj@sandia.gov (CAT).We have developed a multiplexed time-and photon-energy-resolved photoionization mass spectrometer for the study of the kinetics and isomeric product branching of gas phase, neutral chemical reactions. The instrument utilizes a side-sampled flow tube reactor, continuously tunable synchrotron radiation for photoionization, a multi-mass double-focusing mass spectrometer with 100% duty cycle, and a time-and positionsensitive detector for single ion counting. This approach enables multiplexed, universal detection of molecules with high sensitivity and selectivity. In addition to measurement of rate coefficients as a function of temperature and pressure, different structural isomers can be distinguished based on their photoionization efficiency curves, providing a more detailed probe of reaction mechanisms. The multiplexed 3-dimensional data structure

The reactions of H atoms with methane, four chlorinated methanes, and isobutene have been studied experimentally using the discharge flow/resonance fluorescence technique over wide ranges of temperatures. The rate constants were obtained in direct experiments as functions of temperature. The experimentally obtained activation energies of the reactions of H atoms with chlorinated methanes demonstrate a correlation with the enthalpies of the reactions. Transition state theory reaction models were created on the basis of ab initio calculations, the Marcus expression for correlation between reaction barriers and reaction energetics, and analysis of experimental data. It is demonstrated that the formalism based on the Marcus expression adequately describes the observed temperature dependencies of the rate constants of the overall reactions. According to the models, abstraction by H atoms of hydrogen atoms from chloromethanes is an important process accounting for significant fractions of the overall rate constants. The models result in expressions for the rate constants of Cl and H atom abstraction channels and the corresponding reverse reactions over wide ranges of temperatures.