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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We present a direct ab initio dynamics study on the hydrogen abstraction reaction CH2O + HO2 --> CHO + H2O2, which is predicted to have four possible reaction channels caused by different attacking orientations of HO2 radical to CH2O. The structures and frequencies at the stationary points and the points along the minimum energy paths (MEPs) of the four reaction channels are calculated at the B3LYP/cc-pVTZ level of theory. Energetic information of stationary points and the points along the MEPs is further refined by means of some single-point multilevel energy calculations (HL). The rate constants of these channels are calculated using the improved canonical variational transition-state theory with the small-curvature tunneling correction (ICVT/SCT) method. The calculated results show that, in the whole temperature range, the more favorable reaction channels are Channels 1 and 3. The total ICVT/SCT rate constants of the four channels at the HL//B3LYP/cc-pVTZ level of theory are in good agreement with the available experiment data over the measured temperature ranges, and the corresponding three-parameter expression is k(ICVT/SCT) = 3.13 x 10(-20) T(2.70) exp(-11.52/RT) cm3 mole(-1) s(-1) in the temperature range of 250-3000 K. Additionally, the flexibility of the dihedral angle of H2O2 is also discussed to explain the different experimental values.
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PMID:Direct dynamics study on the hydrogen abstraction reaction CH2O + HO2 --> CHO + H2O2. 1636 58

We present a systematic direct ab initio dynamics investigation of the reaction between N2H4 and F atom, which is predicted to have three possible reaction channels. The structures and frequencies at the stationary points and the points along the minimum energy paths (MEPs) of all reaction channels were calculated at the UB3LYP/6-31+G(d,p) level of theory. Energetic information of stationary points and the points along the MEPs was further refined by means of the CCSD(T)/aug-cc-pVTZ method. The calculated results revealed that the first two primary channels (N2H4+F-->N2H3+HF) are equivalent and occur synchronously via the formation of a pre-reaction complex with Cs symmetry rather than via the direct H abstraction. The pre-reaction complex then evolves into a hydrogen-bonding intermediate through a transition state with nearly no barrier and a high exothermicity, which finally makes the intermediate further decompose into N2H3 and HF. Another reaction channel of minor role (N2H4+F-->NH2F+NH2) was also found during the calculations, which has the same Cs pre-reaction complex but forms NH2F and NH2 via another transition state with high-energy barrier and low exothermicity. The rate constants of these channels were calculated using the improved canonical variational transition state theory with the small-curvature tunneling correction (ICVT/SCT) method. The three-parameter ICVT/SCT rate constant expressions of k(ICVT/SCT) at the CCSD(T)/aug-cc-pVTZ//UB3LYP/6-31+G(d,p) level of theory within 220-3000 K were fitted as (7.64x10(-9))T (-0.87) exp(1180/T) cm3 mole-1 s-1 for N2H4+F-->N2H3+HF and 1.45x10(-12)(T/298)(2.17) exp(-1710/T) cm3 mole-1 s-1 for N2H4+F-->NH2F+NH2.
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PMID:Direct dynamics study on the reaction of N2H4 with F atom: a hydrogen abstraction reaction? 1703 57