Katarzyna Brudnik

Mechanism of the gas-phase decomposition of trifluoro-, trichloro-, and tribromomethanols in the presence of hydrogen halides

Ab initio calculations at the G2 level were used in a theoretical analysis of the kinetics of the decomposition of trifluoro-, trichloro-, and tribromomethanols. The high-pressure limiting rate coefficients kdiss,∞ for the thermal dissociation of CF3OH, CCl3OH, and CBr3OH were calculated using the conventional transition state theory. The results of potential surface calculations show that in the presence of the hydrogen halides HX (X = F, Cl, and Br), considerably lower energy pathways are accessible for the decomposition of CF3OH, CCl3OH, and CBr3OH. The mechanism of the reactions appears to be complex and consists of three consecutive elementary processes with the formation of pre- and post-reaction adducts. The presence of hydrogen halides considerably decreases the energy barrier for the bimolecular decomposition of the alcohols CF3OH, CCl3OH, and CBr3OH. Results of this study indicate that hydrogen halides can considerably accelerate the homogeneous decomposition of perhalogenated methanols when they are present in the reaction area at sufficiently high concentrations. However, the atmospheric concentrations of hydrogen halides are too small for efficient removal of atmospheric CF3OH, CCl3OH, and CBr3OH.

Kinetics of the formation reactions of trifluoromethanol and trifluoromethyl hypohalites in the gas phase

Abstract The CF 3 OX molecules (X=H, F, Cl and Br) can be formed in the atmosphere by the recombination CF 3 +OX and CF 3 O+X reactions. In this study we present results of the theoretical analysis on the kinetics and thermochemistry of this class of reactions. Molecular properties of the reactants and products were derived from ab initio calculations. Relative total energies were examined using G2 methodology. The high-pressure limiting rate constants were evaluated using one of the versions of the statistical adiabatic channel model. The calculated rate constants allow a description of the kinetics of the reactions under investigation in the temperature range of 200–500 K.

Theoretical study of the kinetics of reactions of the monohalogenated methanes with atomic chlorine

Ab initio calculations at the G2 level were used in a theoretical description of the kinetics and mechanism of the hydrogen abstraction reactions from fluoro-, chloro- and bromomethane by chlorine atoms. The profiles of the potential energy surfaces show that mechanism of the reactions under investigation is complex and consists of two - in the case of CH3F+Cl - and of three elementary steps for CH3Cl+Cl and CH3Br+Cl. The heights of the energy barrier related to the H-abstraction are of 8–10 kJ mol−1, the lowest value corresponds to CH3Cl+Cl and the highest one to CH3F+Cl. The rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The kinetic equations derived in this study

Kinetics of the formation reactions of trichloro-and tribromomethyl hypohalites and alcohols in the gas-phase : Theoretical study

\begin{array}{*{20}c} {k\left( {\mathrm{C}{{\mathrm{H}}_3}\mathrm{F}+\mathrm{Cl}} \right)=6.75\times 1{0^{-12 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{2.12 }}\times\exp (-900/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_3}\mathrm{Cl}+\mathrm{Cl}} \right)=6.97\times 1{0^{-12 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.73 }}\times\exp (-795/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_3}\mathrm{Br}+\mathrm{Cl}} \right)=6.26\times 1{0^{-12 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.82 }}\times\exp (-795/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ \end{array}

Theoretical study of the kinetics of chlorine atom abstraction from chloromethanes by atomic chlorine

and

Kinetic study of the reaction of chlorine atoms with dichloromethane and D-dichloromethane in the gas phase

\begin{array}{*{20}c} {k\left( {\mathrm{C}{{\mathrm{H}}_2}\mathrm{F}+\mathrm{HCl}} \right)=2.88\times 1{0^{-13 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{2.02 }}\times\exp (-1255/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_2}\mathrm{Cl}+\mathrm{HCl}} \right)=2.42\times 1{0^{-13 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.57 }}\times\exp (-2100/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ {k\left( {\mathrm{C}{{\mathrm{H}}_2}\mathrm{Br}+\mathrm{HCl}} \right)=2.21\times 1{0^{-13 }}\times {{{\left( {\mathrm{T}/300} \right)}}^{1.69 }}\times\exp (-1485/\mathrm{T})}{\mathrm{c}{{\mathrm{m}}^3}\mathrm{molecul}{{\mathrm{e}}^{-1 }}{{\mathrm{s}}^{-1 }}} \\ \end{array}