Computational studies on the kinetics and mechanisms for NH3 reactions with ClOx (x=0-4) radicals

Department of Chemistry, Emory University, Atlanta, Georgia, United States
The Journal of Physical Chemistry A (Impact Factor: 2.78). 03/2007; 111(4):584-90. DOI: 10.1021/jp065397t
Source: PubMed

ABSTRACT Kinetics and mechanisms for NH3 reactions with ClOx (x = 0-4) radicals have been investigated at the G2M level of theory in conjunction with statistical theory calculations. The geometric parameters of the species and stationary points involved in the reactions have been optimized at the B3LYP/6-311+G(3df,2p) level of theory. Their energetics have been further refined with the G2M method. The results show that the H-abstraction process is the most favorable channel in each reaction and the barriers predicted in decreasing order are OClO > ClO > Cl > ClO3 > ClO4. All reactions were found to occur by hydrogen-bonding complexes; the rate constants for these complex metathetical processes have been calculated in the temperature range 200-2000 K by the microcanonical VTST and/or RRKM theory (for ClO4 + NH3) with Eckart tunneling and multiple reflection corrections. The predicted rate constants are in good agreement with the available experimental data.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The insertion reaction mechanism of CBr2 with CH3CHO has been studied by using the B3LYP/6-31G(d) method. The geometries of reactions, transition state and products were completely optimized. All the energy of the species was obtained at the CCSD(T)/6-31G(d) level. All the transition state is verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The results show that the propionaldehyde (HP1) is the main product of CH2 insertion with CH3CHO. The calculated results indicated that all the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CBr2 not only can insert the Cα-H [reaction I(1)]) but also can react with Cβ-H [reaction II(1)]. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of I(1) and II(1) in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature rang is 250 to 1750 K and 250 to 1600 K at 1.0 atm for I(1) and II(1) respectively. The rate constant and equilibrium constant are distinct in the range from 250 to 1000 K so that I(1) more easily occurs, while the reactions are not selected in the temperature range of 1000–1600 K.
    Chinese Science Bulletin 01/2008; 53(5):718-726. DOI:10.1007/s11434-008-0056-4 · 1.37 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Using ab initio information at the CCSD(T)/cc-pVTZ level, the reaction path for the Cl + NH(3) hydrogen abstraction reaction was traced, and the coupling terms between the reaction coordinate and the normal modes were analyzed along it. Two intermediate complexes were located in the entry channel and characterized close to the reactants. One of them presents a typical Cl...H-N bond, while the second presents a two-center/three-electron Cl[symbol:see text]N bond. Both complexes are on the reaction path and contribute to the final rate constants. With this information, the rate constants were calculated over the temperature range 200-2000 K, using variational transition state theory with multidimensional tunneling contributions, and were found to reproduce the experimental evidence in the common temperature range. Finally, analysis of the coupling terms showed qualitatively that vibrational excitation of the N-H stretch and the bending and umbrella modes in the reactant NH(3) enhances the forward thermal rate constants, and that, in the products, the H-Cl stretch mode and the bending mode in NH(2) could appear vibrationally excited, although the randomization of the energy in the well in the exit channel might diminish this excitation.
    The Journal of Physical Chemistry A 03/2010; 114(12):4418-26. DOI:10.1021/jp911664t · 2.78 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mechanisms for the reactions of ClO with C(2)H(2) and C(2)H(4) have been investigated at the CCSD(T)/CBS level of theory. The results show that in both systems, the interaction between the Cl atom of the ClO radical and the triple and double bonds of C(2)H(2) and C(2)H(4) forms prereaction van der Waals complexes with the O-Cl bond pointing perpendicularly toward the π-bonds, both with 2.1 kcal/mol binding energies. The mechanism is similar to those of the HO-C(2)H(2)/C(2)H(4) systems. The rate constants for the low energy channels have been predicted by statistical theory. For the reaction of ClO and C(2)H(2), the main channels are the production of CH(2)CO + Cl (k(1a)) and CHCO + HCl (k(1b)), with k(1a) = 1.19 × 10(-15)T(1.18) exp(-5814/T) and k(1b) = 6.94 × 10(-21) × T(2.60) exp(-6587/T) cm(3) molecule(-1) s(-1). For the ClO + C(2)H(4) reaction, the main pathway leads to C(2)H(4)O + Cl (k(2a)) with the predicted rate constant k(2a) = 2.13 × 10(-17)T(1.52) exp(-3849/T) in the temperature range of 300-3000 K. These rate constants are pressure-independent below 100 atm.
    The Journal of Physical Chemistry A 12/2010; 114(51):13395-401. DOI:10.1021/jp107596y · 2.78 Impact Factor
Show more