A Diode Laser Study of the Product Branching Ratios of the CH + NO 2 Reaction

et al. 2005

The radical-molecule reaction mechanism of CH3 with NOx (x = 1, 2) has been explored theoretically at the B3LYP/6-311Gd,p and MC-QCISD (single-point) levels of theory. For the singlet potential energy surface (PES) of the CH3 + NO2 reaction, it is found that the carbon to middle nitrogen attack between CH3 and NO2 can form energy-rich adduct a (H3CNO2) with no barrier followed by isomerization to b1 (CH3ONO-trans), which can easily convert to b2 (CH3ONO-cis). Subsequently, starting from b (b1, b2), the most feasible pathway is the direct N-O bond cleavage of b (b1, b2) leading to P1 (CH3O + NO) or the 1,3-H-shift and N-O bond rupture of b1 to form P2 (CH2O + HNO), both of which may have comparable contribution to the reaction CH3 + NO2. Much less competitively, b2 can take a concerted H-shift and N-O bond cleavage to form product P3 (CH2O + HON). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CH3 + NO2 reaction is expected to be rapid, as is consistent with the experimental measurement in quality. For the singlet PES of the CH3 + NO reaction, the major product is found to be P1 (HCN + H2O), whereas the minor products are P2 (HNCO + H2) and P3 (HNC +H2O). The CH3 + NO reaction is predicted to be only of significance at high temperatures because the transition states involved in the most feasible pathways lie almost above the reactants. Compared with the singlet pathways, the triplet pathways may have less contributions to both reactions. The present study may be helpful for further experimental investigation of the title reactions.

Section: The Singlet Potential Energy Surfacementioning

confidence: 90%

Section: The Singlet Potential Energy Surfacementioning

confidence: 99%

Theoretical study on the reaction mechanism of the methyl radical with nitrogen oxides

Zhang

et al. 2005

“…This point can be well accounted for by the overall barrierless isomerization and dissociation processes of this reaction. However, it is still much slower than the CH + NO 2 reaction 22 with k = 1.7 × 10 −10 cm 3 molecule −1 s −1 . The different reactivity can be explained by comparison of the potential energy surface between CH + NO 2 and CF + NO 2 reactions.…”

Section: Mechanismmentioning

confidence: 95%

“…We note that the product distributions of the CH + NO 2 reaction have been recently measured. 22 The major product channel was found to be H + CO + NO or HNO + CO, which together account for 92 ± 4% of the total rate constant, whereas the minor product channel is HCO + NO, accounting for 8 ± 4%. Very recently, we have carried out a detailed theoretical investigation 23 on the singlet potential energy surface of the reaction CH + NO 2 .…”

mentioning

confidence: 92%

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Theoretical study on reaction mechanism of the CF radical with nitrogen dioxide

Tao

et al. 2001

ABSTRACT:The singlet potential energy surface of the [CFNO 2 ] system is investigated at the B3LYP and CCSD(T) (single-point) levels to explore the possible reaction mechanism of CF radical with NO 2 . The top attack of C-atom of CF radical at the N-atom of NO 2 molecule first forms the adduct isomer FCNO 2 1 followed by oxygen-shift to give trans-OC(F)NO 2 and then to cis-OC(F)NO 3. Subsequently, the most favorable channel is a direct dissociation of 2 and 3 to product P 1 FCO + NO. The second and third less favorable channels are direct dissociation of 3 to product P 2 FNO + CO and isomerization of 3 to a complex NOF. . .CO 4, which can easily dissociate to product P 3 FON + CO, respectively. The large exothermicity released in these processes further drives most of the three products P 1 , P 2 , and P 3 to take secondary dissociation to the final product P 12 F + CO + NO. Another energetically allowed channel is formation of product P 4 1 NF + CO 2 , yet it is much less competitive than P 1 , P 2 , P 3 , and P 12 . The present calculations can well interpret one recent experimental fact that the title reaction is quite fast yet still much slower than the analogous reaction CH + NO 2 . Also, the results presented in this article may be useful for future product distribution analysis of the title reaction as well as for the analogous CCl and CBr reactions.

Theoretical study on the mechanism of the ¹CHCl + NO₂ reactions

Zhang

et al. 2004

The radical-molecule reaction mechanism of (1)CHCl with NO(2) has been explored theoretically at the B3LYP/6-311G(d, p) and CCSD(T)/6-311G(d, p) (single-point) levels of theory. Thirteen minimum isomers and 29 transition states are located. The initial association between (1)CHCl and NO(2) proceeds most likely through the carbon-to-middle-nitrogen attack leading to an energy-rich adduct a (HClCNO(2)), which is found to be a barrierless process. Staring from a, the most feasible channel is to undergo a concerted O-shift and C--N bond rupture leading to product P(2) (NO + HClCO). The minor product pathways are the direct O-extrusion of a to P(3) (O + HClCNO-cis) as well as the 1,3-H-shift of a to isomer b (ClCNOOH) followed by a concerted OH-shift leading to d (HOClCNO), which will dissociate to product P(8) (NO + ClCOH) via C--N cleavage. Because the transition states and isomers involved in the most feasible channel all lie below the reactants, the title reaction is expected to be rapid, as is consistent with the measured rate constant at 296 K. The comparison with the analogous reactions (3)CH(2) + NO(2) are discussed. The present study may be useful for further experimental investigation of the title reaction.