The reaction of chlorine atoms withhighly vibrationally excited HCN

A newly developed Doppler-selected time-of-flight ͑a 3D͒ method was applied to map out for the first time the vibrational-specific angular distributions of the DCN product from the title reaction. A tentative vibrational assignment was given for the observed structures. It was found that the nascent DCN is formed with substantial excitations in both C-D stretch and DCN bend modes. While the pure C-D stretch and those associated with low bend excitations are predominantly backward scattered, the highly excited DCN in both modes also exhibit a substantial forward scattered component in the angular distribution.

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confidence: 89%

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confidence: 99%

Direct mapping of vibrational-specific angular distributions of the polyatomic reaction product: CN+D2→DCN+D

Lai

Wang

Chil

et al. 1996

“…A growing body of experimental evidence indicates, however, that the vibration of the nonreacting bond does not always play the role of a spectator in vibrationally excited reactions. In the reaction of ClϩHCN, the groups of Crim 17,18 and Gericke 19,20 demonstrated that vibrational excitation of the C-H stretch led to significant vibrational excitation of the CN fragment, hinting that the CN fragment acts as a participant, not a spectator. Although the cause of this result is still under debate, 18 -22 one proposed explanation is that the ClϩHCN reaction occurs via a complex that randomizes the prepared vibrational motion into other degrees of freedom.…”

Section: Introductionmentioning

confidence: 98%

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

Bechtel

Kim

Camden

et al. 2004

The title reaction is investigated by co-expanding a mixture of Cl2 and CH2D2 into a vacuum chamber and initiating the reaction by photolyzing Cl2 with linearly polarized 355 nm light. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D2 prepared in a local mode containing two quanta in one C-H oscillator /2000>- or in a local mode containing one quantum each in two C-H oscillators /1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. The Cl+CH2D2/2000>- reaction yields methyl radical products primarily in their ground state, whereas the Cl+CH2D2/1100> reaction yields methyl radical products that are C-H stretch excited. The HCl(v=1) rotational distribution from the Cl+CH2D2/2000>- reaction is significantly hotter than the HCl(v=1) rotational distribution from the Cl+CH2D2/1100> reaction, and the HCl(v=1) differential cross-section (DCS) of the Cl+CH2D2/2000>- reaction is more broadly side scattered than the HCl(v=1) DCS of the Cl+CH2D2/1100> reaction. The results can be explained by a simple spectator model and by noting that the /2000>- mode leads to a wider cone of acceptance for the reaction than the /1100> mode. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction.

“…10,11 They find a significant amount of vibrationally excited CN in the ClϩHCN reaction but much less in the OϩHCN and HϩHCN reaction. Their conclusion is that intermediate complex formation is much more important for the ClϩHCN reaction than for the H, OϩHCN reactions.…”

Section: Introductionmentioning

confidence: 98%

Potential energy surface and quasiclassical trajectory studies of the CN+H2 reaction

Horst

Schatz

Harding

1996

103

We present dynamical studies of the CNϩH 2 reaction based on an empirical potential energy surface that is derived from high quality ab initio calculations. The ab initio calculations, which use a multireference configuration interaction method with large correlation consistent basis sets, indicate that the linear HHCN barrier is about 4.3 kcal/mol above CNϩH 2 , and that there is no reaction path which connects CNϩH 2 to the stable intermediate H 2 CN, although there is a path for dissociation of H 2 CN to HϩHCN. The empirical surface is written as a sum of two-, three-, and four-body terms, with the two-and three-body terms for HCN based on an accurate global surface that describes both the HCN and HNC force fields. The four-body terms are developed so as to describe the HHCN linear saddle point and the H 2 CN minimum accurately, as well as dissociation of H 2 CN into HCNϩH, and the ridge which separates the abstraction and H 2 CN dissociation pathways. Other features of the potential surface, such as the HCNH cis and trans minima, and the pathways leading to the formation of HNCϩH are also described, though less accurately. Three different choices for the HHCN saddle point properties are considered. We find that the surface which matches the ab initio barrier energy most accurately gives rate constants that are too low. Much better agreement is obtained using a 3.2 kcal/mol barrier. The trajectory results show typical dependence of the CNϩH 2 reactive cross sections on initial translational energy and initial vibration/rotation state, with CN behaving as a spectator and H 2 playing an active role in the reaction dynamics. Analysis of the HϩHCN products indicates that both the C-H stretch and bend modes are significantly excited, with bend excitation showing strong sensitivity to the saddle point properties and to reagent translational energy. At translational energies below 20 kcal/mol, direct H abstraction is strongly favored over addition elimination.