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Theoretical Analysis of the Kinetics of the Reaction of Methyl Mercaptan with Nitrogen Dioxide in the Gas Phase

Brudnik B., Wójcik-Pastuszka D., Jodkowski J. T.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 6

1203-1221

EN

In this study a theoretical analysis of the kinetics and thermochemistry of the gas phase reaction between methyl mercaptan and nitrogen dioxide is presented. The molecular properties (optimized geometries, vibrational levels, and rotational constants) of the reactants and products were derived from ab in itio calculations. The relative total energies of the molecular structures taking part in the reaction kinetics were examined at the G3 level. The rate constants of the elementary steps and their dependence on temperature were evaluated using transition-state theory and a version of the statistical adiabatic channel model. The mechanism of the reaction CH3SH + NO2 is complex and the first elementary step is related to hydrogen abstraction. The derived analytical expressions for the rate constants k1a = 7.9 x 10–15 x (T/300)1.90 x exp(–8190/T) and k1b = 6.0 x 10–13 x (T/300)1.94 x exp(–16290/T) cm3 molecule–1 s–1 de scribe the kinetics of the hy - drogen abstraction reactions CH3SH + NO2 rightwards arrow CH3S + HNO2 (1a) and CH3SH + NO2 rightwards arrow CH2SH + HNO2 (1b), respectively, in the temperature range of 200–500 K. The CH3S and CH2SH radicals formed can undergo subsequent radical-radical (2a–c) and radical-NO2 (3a,b) recombination reactions with rates determined by the high-pressure limiting rate constant, expressed as k2a,Y(CH3S + CH3S) = 4.0×10–11×(T/300)0.20, k2b,infinity(CH3S + CH2SH) = 1.2×10–10×(T/300)0.15, k2c,infinity(CH2SH + CH2SH) = 6.7×10–11×(T/300)0.19, k3a,infinity(CH3S + NO2) = 1.3×10–11×(T/300)0.19, and k3b,infinity(CH2SH + NO2) = 2.6×10–11×(T/300)0.23 cm3 molecule–1 s–1. Values of the calculated rate constants are in good agreement with available results of kinetic measurements.

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Spectrokinetic Study of the Reaction System of 2NO2"N2O4 with Butanols Between 320-358 K in the Gas Phase

Wójcik-Pastuszka D., Jodkowski J. T.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 1

131-143

EN

Spectrokinetic studies of the gas-phase equilibrium between nitrogen tetroxide and butanols in the reaction system 2NO2"N2O4 (1, 2), N2O4+ROH"RONO+HNO3 (3, 4) have been undertaken in the temperature range 298-358 K. The products - RONO (n-butyl-ONO, sec-butyl-ONO, iso-butyl-ONO and tert-butyl-ONO) - were identified by their UV spectra and the values of the maxima UV absorption cross sections were determined in the range 320-420 nm at 298 K. The temperature dependences of both the forward and reverse rate constants, k3 and k4, were obtained. The extrapolated values of the forward rate constants are 10-18 k3av /cm3 molec-1 s-1 3.9 plus-minus 1.0; 1.7 plus-minus 0.3; 4.2 plus-minus 0.8; 5.7 plus-minus 1.1 and the reverse rate constants are 10-20 k4av /cm3 molec-1 s-1 0.3plus-minus 0.1; 2.3 plus-minus 0.6; 0.4 plus-minus 0.1; 2.3 plus-minus 0.6 at 298 K for the reaction of NO2/N2O4 with n-butanol, sec-butanol, iso-butanol and tert-butanol, respectively. The activation energy for the forward E3 and for the reverse E4 reaction were derived.

3

Theoretical study on the kinetics and mechanism of reactions of halogen atoms with trifluoromethanol

Brudnik K., Jodkowski J. T., Ratajczak E.

Bulletin of the Polish Academy of Sciences. Chemistry

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2003

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Vol. 51, No. 2

77-91

EN

Quantum mechanical ab initio calculations have been performed at various levels of theory to study kinetics of the reactions of fluorine, chlorine and bromine atoms with trifluoromethanol. Total energies were improved by using Gaussian-2 (G2) methodology. It is shown that the considered reactions proceed with formation of intermediate complexes. The mechanism of the reactions studied appears to be more complex and may consist of three elementary steps. The heights of the calculated energy barriers explain the differences of the reactivity of F, C1 and Br atoms towards CFsOH. The rate constants and their temperature dependence for the reactions CFsOH + X (fcx) and CFaO + HX (kfix) were calculated. The derived analytical expressions [chemical formulas] allow the description of the kinetics of the reactions under investigation. This is of considerable importance for the chemical modelling studies because of the lack of experimental measurements.