Quantum Chemical and Statistical Rate Investigation of the CF2(a3B1) + NO(X2) Reaction: A F
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- 作者：Thanh Lam Nguyen ; Shaun A. Carl ; Minh Tho Nguyen ; Jozef Peeters
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：July 26, 2007
- 年：2007
- 卷：111
- 期：29
- 页码：6628 - 6636
- 全文大小：221K
- 年卷期：v.111,no.29(July 26, 2007)
- ISSN：1520-5215
文摘
The reaction of CF2(a3B1) with NO(X2
) was theoretically investigated using the B3LYP, MP2, CCSD(T),G2M, CASSCF, and CASPT2 quantum chemical methods with various basis sets including 6-31G(d), 6-311G(d), 6-311+G(3df), cc-pVDZ, and cc-pVTZ. In agreement with the experimental kinetic data, the CF2(a3B1)+ NO(X2) reaction is found to proceed via a fast, barrier-free combination. This process, occurring on thedoublet potential energy surface, leads to the electronically excited adduct F2C-NO(22A' '), which readilyundergoes a surface hopping to the 12A' electronic surface, with a Landau-Zener transition probabilityestimated to be close to 90% per C-N vibration. The metastable adduct F2C-NO(12A') can then eitherspontaneously decompose into CF2(X1A1) + NO(X2) in a direct chemical quenching mechanism or relaxto its ground-state equilibrium structure F2CNO(X2A'). The product distribution resulting from the latter,chemically activated intermediate was evaluated by solution of the master equation (ME), under differentreaction conditions, using the exact stochastic simulation method; microcanonical rate constants were computedusing Rice-Ramsperger-Kassel-Marcus (RRKM) theory, based on the potential energy surfaces (PESs)constructed using both G2M and CASPT2 methods. The RRKM/ME analysis reveals that the hot F2CNO(X2A') rapidly fragments almost exclusively to the same products as above, CF2(X1A1) + NO(X2), whichamounts to an indirect chemical quenching mechanism. The reaction on the quartet PES is unlikely to besignificant except at very high temperatures. The high crossing probability (up to 90%) between the two"avoided" doublet PESs points out the inherent difficulty in treating chemically activated reactions with fast-moving nuclei within the Born-Oppenheimer approximation.
) was theoretically investigated using the B3LYP, MP2, CCSD(T),G2M, CASSCF, and CASPT2 quantum chemical methods with various basis sets including 6-31G(d), 6-311G(d), 6-311+G(3df), cc-pVDZ, and cc-pVTZ. In agreement with the experimental kinetic data, the CF2(a3B1)+ NO(X2) reaction is found to proceed via a fast, barrier-free combination. This process, occurring on thedoublet potential energy surface, leads to the electronically excited adduct F2C-NO(22A' '), which readilyundergoes a surface hopping to the 12A' electronic surface, with a Landau-Zener transition probabilityestimated to be close to 90% per C-N vibration. The metastable adduct F2C-NO(12A') can then eitherspontaneously decompose into CF2(X1A1) + NO(X2) in a direct chemical quenching mechanism or relaxto its ground-state equilibrium structure F2CNO(X2A'). The product distribution resulting from the latter,chemically activated intermediate was evaluated by solution of the master equation (ME), under differentreaction conditions, using the exact stochastic simulation method; microcanonical rate constants were computedusing Rice-Ramsperger-Kassel-Marcus (RRKM) theory, based on the potential energy surfaces (PESs)constructed using both G2M and CASPT2 methods. The RRKM/ME analysis reveals that the hot F2CNO(X2A') rapidly fragments almost exclusively to the same products as above, CF2(X1A1) + NO(X2), whichamounts to an indirect chemical quenching mechanism. The reaction on the quartet PES is unlikely to besignificant except at very high temperatures. The high crossing probability (up to 90%) between the two"avoided" doublet PESs points out the inherent difficulty in treating chemically activated reactions with fast-moving nuclei within the Born-Oppenheimer approximation.