Photodissociation of C2H at 193 nm: Branching ratios for the formation of C2 in the X 1Σg+, A 1Πu, and B′ 1Σg+ states

Sorkhabi, Osman; Blunt, Victor M.; Lin, Hai–Qing; Xu, Duo; Wrobel, Jacek D.; Price, Richard A.; Jackson, William M.

doi:10.1063/1.475281

Cited by 28 publications

(26 citation statements)

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“…Hence, excitation of the Swan band system at formation is an ineffective pump relative to the visible fluorescence. The more since only 5% of C 2 resulting from photo-dissociation of C 2 H is formed in the triplet state (Sorkhabi et al 1997;Wodtke & Lee 1985).…”

Section: Discussionmentioning

confidence: 99%

C₂emission features in the Red Rectangle

Wehres

Romanzin

Linnartz

et al. 2010

A&A

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Context. The Red Rectangle proto-planetary nebula (HD 44179) is known for a number of rather narrow emission features superimposed on a broad extended red emission (ERE) covering the 5000-7500 Å regime. The origin of these emission features is unknown. Aims. The aim of the present work is to search for potential carriers by combining new observational and laboratory data. This also allows to interpret spectral emission features in terms of actual physical conditions like temperature and density constraints and to trace chemical processes in the outflows of the Red Rectangle. Methods. Observational spectra have been obtained with the EMMI-NTT at offsets of 3 , 6 , 7 , 11 , 16 and 20 distance to the central star HD 44179. The spectra are compared to the outcome of a time-gated laser induced fluorescence laboratory study of an expanding acetylene plasma using a special supersonic pin-hole discharge source. With this set-up the hydrocarbon chemistry in the Red Rectangle nebula is simulated under laboratory controlled conditions. The plasma source has the unique feature to generate electronically and vibrationally excited species at low rotational temperatures. The comparison is facilitated by a simple model for fluorescent emission in the nebula. Results. Two of the astronomically observed narrow emission bands can be assigned as originating from unresolved rovibronic progressions within the d 3 Π g → a 3 Π u Swan system of the C 2 radical. The band appearance corresponds to a rotational temperature between 200 and 1000 K. The emission is driven by absorption in the C 2 Phillips bands followed by intersystem crossing from the singlet to the triplet state and pumping in the Swan bands. Conclusions. These observations imply an active (photo)chemistry in the ejecta of the Red Rectangle.

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Section: Discussionmentioning

confidence: 99%

C₂emission features in the Red Rectangle

Wehres

Romanzin

Linnartz

et al. 2010

A&A

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“…56 The population of rotational state J′ of a vibrational state v' in an excited electronic state Λ′ is denoted N(Λ′, v′, J′) and is given by the following expression for a bimodal rotational distribution;…”

Section: 4mentioning

confidence: 99%

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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“…The ethynyl radical, C 2 H, has long been a subject to experimental [1][2][3][4][5][6] and theoretical investigations, [6][7][8][9][10][11][12][13][14][15] which can be attributed to its important role in combustion, 16 its prominent presence in astrophysics as a major source of C 2 in comets and interstellar media, 17 and for understanding the photochemistry and spectroscopy of this molecule. The strong vibronic interaction between the ground state X 2 ⌺ ϩ ( 4 5 1 ) and the first excited state A 2 ⌸( 3 5 2 ) of C 2 H, that are separated only by 3600 cm Ϫ1 , restrains the definite spectroscopic characterization of C 2 H radical.…”

Section: Introductionmentioning

confidence: 99%

Photodissociation of CCH: Classical trajectory calculations involving seven electronic states

Apaydın

Fink

Jackson

2004

The Journal of Chemical Physics

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The photodissociation dynamics of ethynyl radical, C(2)H, involving seven electronic states is studied by classical trajectory calculations. Initial values of the trajectories are selected based on relative absorption intensities calculated by Mebel et al. The energies and the derivatives are interpolated by three-dimensional cubic spline interpolator using an extended data pool. Mean square errors and standard deviations in interpolation of energies for 450 data points are found to be in the range 3.1 x 10(-6)-1.4 x 10(-5) and 1.7 x 10(-3)-3.8 x 10(-3) hartrees, respectively. The photofragments of C(2) and H are produced mainly in the X (1)Sigma(g) (+), a (3)Pi(u), b (3)Sigma(g) (-), c (3)Sigma(u) (+), A (1)Pi(u), B (1)Delta(g) electronic states of C(2) as product. The avoided crossings do not appear to be in the main dissociation pathways. The internal distributions are in good accord with the experimental results where comparison is possible, suggesting that the fragmentation mechanism of C(2)H(2) into C(2) and H is a two step process involving C(2)H radical as an intermediate with a life time long enough to allow complete collection of the phase space in the experiments.

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Photodissociation of C2H at 193 nm: Branching ratios for the formation of C2 in the X 1Σg+, A 1Πu, and B′ 1Σg+ states

Cited by 28 publications

References 59 publications

C₂emission features in the Red Rectangle

C₂emission features in the Red Rectangle

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

Photodissociation of CCH: Classical trajectory calculations involving seven electronic states

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Photodissociation of C2H at 193 nm: Branching ratios for the formation of C2 in the X 1Σg+, A 1Πu, and B′ 1Σg+ states

Cited by 28 publications

References 59 publications

C2emission features in the Red Rectangle

C2emission features in the Red Rectangle

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

Photodissociation of CCH: Classical trajectory calculations involving seven electronic states

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Product

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C₂emission features in the Red Rectangle

C₂emission features in the Red Rectangle

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