The VUV photodissociation CH3 → CH(A2Δ and B2Σ− + H2

Kassner, Ch.; Stuhl, F.

doi:10.1016/0009-2614(94)00389-0

Cited by 15 publications

(5 citation statements)

References 27 publications

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“…whose quantum yields are not clear. Channel (A.3) is observed at 2163 Å by Wilson et al (1994), at 1933Å by North et al (1995, and at 2125 Å by Wu et al (2004), while channel (A.4) is observed through fluorescence of CH at λ > 1050 Å by Kassner & Stuhl (1994). In the absence of better constraints we have assumed a quantum yield of 50 % for each channel.…”

Section: A1 Chmentioning

confidence: 99%

The chemistry of disks around T Tauri and Herbig Ae/Be stars

Agúndez

Roueff

Petit

et al. 2018

A&A

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Section: A1 Chmentioning

confidence: 99%

The chemistry of disks around T Tauri and Herbig Ae/Be stars

Agúndez

Roueff

Petit

et al. 2018

A&A

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“…For the latter pathway, the formation of CH 3 + CN(X 2 Σ + ) results in an excess energy of 10.80 eV when h ν = 16 eV, because Δ = 5.26 eV to form these products. The predissociation of high-lying Rydberg levels of CH 3 * into CH(A 2 Δ) + H 2 has been detected elsewhere . The thermodynamic threshold for forming CH(A 2 Δ, v ‘ = 2) + H 2 from the methyl radical is calculated as 8.38 eV from the minimum photon energy to give CH(A 2 Δ) signal from CH 3 in the previous study (7.55 eV) 64 plus the 0.83 eV required to populate CH(A 2 Δ) up to the v ‘ = 2 level.…”

Section: Discussionmentioning

confidence: 75%

“…Considering the CH 3 + CN(B 2 Σ + ) channel (Δ = 8.45 eV), the internal energy of the CH 3 CN parent molecule at 298 K (0.06 eV) and the extent of vibrational excitation in CN(B 2 Σ + ) observed in the 16 eV spectrum (Figure a), E xs equals 6.70 eV for this channel. Previous studies of the photodissociation of CH 3 show that at least 7.55 eV is required for the CH 3 → CH(A 2 Δ) + H 2 process to occur . Therefore, there is insufficient energy available to form CH(A 2 Δ) by this two step mechanism at h ν = 16 eV, thus requiring the formation of either CH(A 2 Δ) or CN(B 2 Σ + ) by separate dissociation processes at this photon energy.…”

Section: Discussionmentioning

confidence: 98%

“…The predissociation of high-lying Rydberg levels of CH 3 * into CH(A 2 ∆) + H 2 has been detected elsewhere. 64 The thermodynamic threshold for forming CH(A 2 ∆, v′ = 2) + H 2 from the methyl radical is calculated as 8.38 eV from the minimum photon energy to give CH(A 2 ∆) signal from CH 3 in the previous study (7.55 eV) 64 plus the 0.83 eV required to populate CH(A 2 ∆) up to the v′ = 2 level. Therefore, the two step mechanism is viable if a substantial portion of the excess energy is partitioned into the methyl fragment.…”

Section: Cn(b 2 σ + -X 2 σ + ) and Ch(a 2 ∆ -X 2 π) Emission Observedmentioning

confidence: 97%

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State-Resolved Dynamics of the CN(B²Σ⁺) and CH(A²Δ) Excited Products Resulting from the VUV Photodissociation of CH₃CN

et al. 2007

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Fourier transform visible spectroscopy, in conjunction with VUV photons produced by a synchrotron, is employed to investigate the photodissociation of CH 3 CN. Emission is observed from both the CN(B 2 Σ + -X 2 Σ + ) and CH(A 2 ∆-X 2 Π) transitions; only the former is observed in spectra recorded at 10.2 and 11.5 eV, whereas both are detected in the 16 eV spectrum. The rotational and vibrational temperatures of both the CN(B 2 Σ + ) and CH(A 2 ∆) radical products are derived using a combination of spectral simulations and Boltzmann plots. The CN(B 2 Σ + ) fragment displays a bimodal rotational distribution in all cases. T rot (CN(B 2 Σ + )) ranges from 375 to 600 K at lower K′ and from 1840 to 7700 K at higher K′ depending on the photon energy used. Surprisal analyses indicate clear bimodal rotational distributions, suggesting CN(B 2 Σ + ) is formed via either linear or bent transition states, respectively, depending on the extent of rotational excitation in this fragment. CH(A 2 ∆) has a single rotational distribution when produced at 16 eV, which results in T rot (CH(A 2 ∆)) ) 4895 ( 140 K in V′ ) 0 and 2590 ( 110 K in V′ ) 1. From thermodynamic calculations, it is evident that CH(A 2 ∆) is produced along with CN(X 2 Σ + ) + H 2 . These products can be formed by a two step mechanism (via excited CH 3 * and ground state CN(X 2 Σ + )) or a process similar to the "roaming" atom mechanism; the data obtained here are insufficient to definitively conclude whether either pathway occurs. A comparison of the CH(A 2 ∆) and CN(B 2 Σ + ) rotational distributions produced by 16 eV photons allows the ratio between the two excited fragments at this energy to be determined. An expression that considers the rovibrational populations of both band systems results in a CH(A 2 ∆):CN(B 2 Σ + ) ratio of (1.2 ( 0.1):1 at 16 eV, thereby indicating that production of CH(A 2 ∆) is significant at 16 eV. † Part of the special issue "M. C. Lin Festschrift".

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“…It has been observed that at least some channels on the CH 3 and HCCO surfaces are not characterized by strong CH A T B mixing. In the vacuum ultraviolet (VUV) photodissocation of the CH 3 radical, 64 resonances associated with CH 3 Rydberg states produce CH A 2 ∆ as the dominant electronically excited product. Even above the threshold for B 2 Σproduction, it is formed in much lower yield.…”

Section: Discussionmentioning

confidence: 99%

Collision-Partner Dependence of Energy Transfer between the CH A²Δ and B²Σ^- States

2005

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We have investigated experimentally the collision-induced electronic energy transfer between the CH A(2)Delta and B(2)Sigma(-) states with the series of partners He, Ar, H(2), N(2), CO, and CO(2). Single rovibronic states of either of the near-degenerate levels A(2)Delta, v = 1, or B(2)Sigma(-), v = 0, were prepared by laser excitation. Collisional transfer processes were monitored by detecting dispersed, time-resolved fluorescence from the initial and product states. The microscopic rate constants for vibronically resolved transfer between the A(2)Delta and B(2)Sigma(-) states, vibrational relaxation within the A state, and total removal to unobserved final products were determined for each partner. In line with previous work, we find that only CO and H(2) are efficient at total removal of CH A(2)Delta and B(2)Sigma(-), most probably through chemical reaction. CO(2) is notably effective at A(2)Delta state vibrational relaxation, possibly through resonant vibrational energy transfer. All the partners cause transfer between CH A(2)Delta and B(2)Sigma(-). An important new observation is that their efficiencies are well correlated with the strength of long-range attractive forces, as revealed through a positive correlation of the Parmenter-Seaver type. The vibronic branching to A(2)Delta, v = 0 and 1 from B(2)Sigma(-), v = 0 is found to be significantly collision-partner-dependent and not well predicted by energy gap scaling laws. We do not find any enhanced effectiveness in B(2)Sigma(-) to A(2)Delta coupling for those partners which form strongly bound intermediates, suggesting that this specific electronic channel is controlled by different regions of the potential energy surfaces.

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The VUV photodissociation CH3 → CH(A2Δ and B2Σ− + H2

Cited by 15 publications

References 27 publications

The chemistry of disks around T Tauri and Herbig Ae/Be stars

The chemistry of disks around T Tauri and Herbig Ae/Be stars

State-Resolved Dynamics of the CN(B²Σ⁺) and CH(A²Δ) Excited Products Resulting from the VUV Photodissociation of CH₃CN

Collision-Partner Dependence of Energy Transfer between the CH A²Δ and B²Σ^- States

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The VUV photodissociation CH3 → CH(A2Δ and B2Σ− + H2

Cited by 15 publications

References 27 publications

The chemistry of disks around T Tauri and Herbig Ae/Be stars

The chemistry of disks around T Tauri and Herbig Ae/Be stars

State-Resolved Dynamics of the CN(B2Σ+) and CH(A2Δ) Excited Products Resulting from the VUV Photodissociation of CH3CN

Collision-Partner Dependence of Energy Transfer between the CH A2Δ and B2Σ- States

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State-Resolved Dynamics of the CN(B²Σ⁺) and CH(A²Δ) Excited Products Resulting from the VUV Photodissociation of CH₃CN

Collision-Partner Dependence of Energy Transfer between the CH A²Δ and B²Σ^- States