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Computers in Chemistry

Computers in Chemistry. Final Presentation: N 2 H Chris Hamilton. The molecule N 2 H is of great interest in combustion chemistry due to its possible participation as an intermediate in the removal of NO from exhaust gases by reaction with ammonia.

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Computers in Chemistry

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  1. Computers in Chemistry Final Presentation: N2H Chris Hamilton

  2. The molecule N2H is of great interest in combustion chemistry due to its possible participation as an intermediate in the removal of NO from exhaust gases by reaction with ammonia. From Introduction to Quantum Chemistry, M.A. Ratner and G.C. Schatz, chapter 14

  3. However, it is not clear whether N2H is stable enough to participate in kinetic processes at temperatures relevant to combustion. From Introduction to Quantum Chemistry, M.A. Ratner and G.C. Schatz, chapter 14

  4. Three methods were used to find an energy minimum: •Hartree-Fock (6-31G* basis set) •Semi-Empirical, Austin Model 1 (AM1) •Density Functional (B3LYP using 6-31G*) Energies were calculated at fixed N-H bond lengths which were varied to find the energy minimum.

  5. At longer N-H bond lengths N-N-H angle is about 80° • No real interaction at N-H lengths > 2.5 angstroms

  6. As N-H distance is decreased, N-N-H angle increases to approximately 115° at minimum energy • At N-H bond lengths below ≈ 1.07 angstroms, angle increases

  7. Results: Hartree-Fock method Energy minimum at: rNH = 1.07Å NNH angle = 113º E = -109.425 hartrees Saddle point at: rNH = 1.38Å NNH angle = 113º E = -109.403 hartrees

  8. Results: DF method Energy minimum at: rNH = 1.06Å NNH angle = 117º E = -110.030 hartrees Saddle point at: rNH = 1.5Å NNH angle = 118º E = -110.012 hartrees

  9. Is N2H Stable? • Energy of N2H: approximately -109 hartrees • Energy of isolated H2 and N2: -108.841 hartrees

  10. Is N2H Stable? • HF method: 0.022 hartree barrier to dissociation • DF method: 0.018 hartree barrier to dissociation • Appears stable with respect to N2 + H2 by 0.584 hartree (HF) and 1.19 hartree (DF)

  11. Is N2H Stable? • According to one published ab initio study2, N2H is unstable with respect to N2 + H2 by 0.0053 hartree • However, there is a 0.022 hartree barrier to dissociation • Theoretical2 and experimental3 data suggests that the lifetime of this molecule is too short to participate in combustion processes. 2Walch, et. al., J. Chem. Phys. 90, 3230 (1989). 3Curtiss, et.al., Chem. Phys. Lett.103, 437 (1984).

  12. The End • Sources: 1Introduction to Quantum Chemistry, M.A. Ratner and G.C. Schatz, chapter 14. 2Walch, et. al., J. Chem. Phys. 90, 3230 (1989). 3Curtiss, et.al., Chem. Phys. Lett.103, 437 (1984). 4Walch,S.P., J.Chem. Phys. 93, 2384 (1990).

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