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- Quasiclassical study of a termolecular reaction: a more detailed description of the HO2 collisional stabilization processPublication . Mogo, César; Brandão, João; Wang, Wenli; Coelho, Daniela; Rio, CarolinaWe present detailed studies of the collisional stabilization of the HO*2 radical in a mixture of hydrogen atoms and oxygen molecules using molecular dynamic studies and accurate potential energy surfaces. Following previous work on this process's global temperature and pressure dependencies, we analyze each collider's role and estimate specific rate constants and their temperature dependence.
- Experimental and theoretical studies of the gas-phase reactions of O(1D) with H2O and D2O at low temperaturePublication . Hickson, Kevin; Bhowmick, Somnath; Suleimanov, Yury; Brandão, João; Coelho, DanielaHere we report the results of an experimental and theoretical study of the gas-phase reactions between O($^1$D) and H$_2$O and O($^1$D) and D$_2$O at room temperature and below. On the experimental side, the kinetics of these reactions have been investigated over the 50-127 K range using a continuous flow Laval nozzle apparatus, coupled with pulsed laser photolysis and pulsed laser induced fluorescence for the production and detection of O($^1$D) atoms respectively. Experiments were also performed at 296 K in the absence of a Laval nozzle. On the theoretical side, the existing full-dimensional ground X$^1$A potential energy surface for the H$_2$O$_2$ system involved in this process has been reinvestigated and enhanced to provide a better description of the barrierless H-atom abstraction pathway. Based on this enhanced potential energy surface, quasiclassical trajectory calculations and ring polymer molecular dynamics simulations have been performed to obtain low temperature rate constants. The measured and calculated rate constants display similar behaviour above 100 K, showing little or no variation as a function of temperature. Below 100 K, the experimental rate constants increase dramatically, in contrast to the essentially temperature independent theoretical values. The possible origins of the divergence between experiment and theory at low temperatures are discussed.
- Quasiclassical study of a termolecular reaction: Application to the HO2 collisional stabilization processPublication . Mogo, César; Brandão, João; Wang, Wenli; Coelho, Daniela; Rio, CarolinaWe present a multiprocess reaction dynamics program to study the termination reaction H + O-2 + M -> HO2 + M, one main uncertainty source in hydrogen combustion studies. We simulate the behavior of a mixture of hydrogen atoms and oxygen molecules at different conditions of temperature and pressure, using classical mechanics and accurate Potential Energy Surfaces. In this simulation we treat all the reaction channels, including the stabilization step, in the same dynamical procedure. The contribution of the collisional effects on all the reactions is also accounted for. Following the fate of the excited HO2* radical, we analyze the collisional stabilization and estimate the kinetic parameters of the involved reactions. A Lindemann-Hinshelwood type reaction scheme is shown to be able to describe the kinetics of this reaction as a function of pressure and temperature. This way, we propose a procedure to directly study termolecular reactions.