Direct Dynamics Study on the Reaction of N 2 H 4 with F Atom: A Hydrogen Abstraction Reaction?
ABSTRACT 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.
- [Show abstract] [Hide abstract]
ABSTRACT: The reaction of N(2)H(4) with OH has been investigated by quantum chemical methods. The results show that hydrogen abstraction mechanism is more feasible than substitution mechanism thermodynamically. The calculated rate constants agree with the available experimental data. The calculated results show that the variational effect is small at lower temperature region, while it becomes significant at higher temperature region. On the other hand, the small-curvature tunneling effect may play an important role in the temperature range 220-3000 K. Moreover, the calculated rate constants show negative temperature dependence at the temperatures below 500 K, which is in accordance with Vaghjiani's report that slightly negative temperature dependence is found over the temperature range of 258-637 K. The mechanism of the major product (N(2)H(3)) with OH has also been investigated theoretically to understand the title reaction thoroughly.Journal of Computational Chemistry 01/2009; 31(7):1520-7. DOI:10.1002/jcc.21438 · 3.60 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The F + CH(3)NHNH(2) reaction mechanism is studied based on ab initio quantum chemistry methods as follows: the minimum energy paths (MEPs) are computed at the UMP2/6-311++G(d,p) level; the geometries, harmonic vibrational frequencies, and energies of all stationary points are predicted at the same level of theory; further, the energies of stationary points and the points along the MEPs are refined by UCCSD(T)/6-311++g(3df,2p). The ab initio study shows that, when the F atom approaches CH(3)NHNH(2), the heavy atoms, namely N and C atoms, are the favorable combining points. For the two N atoms, two prereaction complexes with C(s) symmetry are generated and there exists seven possible subsequent reaction routes, of which routes 1, 2, 5, and 7 are the main channels. Routes 1, 2, and 5 are associated with HF elimination, with H from the amino group or imido group, and route 7 involves the N-N bond break. Routes 3 and 6 with relation to HF elimination with H from methyl, and route 4 involved the C-N bond break, are all energetically disfavored. For the C atom, the attack of F results in the break of the C-N bond and the products are CH(3)F + NHNH(2). This route is very competitive.The Journal of Physical Chemistry A 02/2011; 115(5):805-14. DOI:10.1021/jp106401r · 2.78 Impact Factor