Direct ab initio dynamics studies of the hydrogen abstraction reactions of hydrogen atom with fluoromethanes
- Univ. of Utah, Salt Lake City, UT (United States)
Halons (chlorofluorobromocarbons) have been widely used as a chemical fire extinguisher in ships, aircraft, and computer rooms; however, their production and use are banned worldwide because of their destructive effects on stratospheric ozone. It is understood that the ozone depletion potential of halons is caused by bromine. As an alternative to halons, hydrofluorocarbons (HFC) have been proposed as fire suppressants. A direct ab initio dynamics study on the gas-phase reactions of atomic hydrogen with different fluoromethanes has been carried out. The thermal rate constants were calculated using canonical variational transition state (CVT) theory augmented by multidimensional semiclassical zero and small curvature tunneling approximations. The potential energy surfaces for the reactions were calculated using hybrid density functional theory, namely, Becke`s half-and-half (BH) nonlocal exchange and the Lee-Yang-Parr (LYP) nonlocal correlation functionals using the cc-pVDZ basis set. The reaction energies and barrier heights were improved by single-point energy calculations along the minimum energy path (MEP) at the spin-projected fourth order Moller-Plesset perturbation theory (PMP4) using the cc-pVTZ basis set. The calculated forward and reverse thermal rate constants are in the good agreement with the experimental data. The electronic effects of fluorine substitution on the rate of this class of reactions are examined.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
- OSTI ID:
- 343566
- Journal Information:
- Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Vol. 103, Issue 13; Other Information: PBD: 1 Apr 1999
- Country of Publication:
- United States
- Language:
- English
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