The intensity distribution in the CH(A2Δ − X2Π) spectrum produced by electron impact on acetylene

doi:10.1016/0022-4073(75)90127-2

Journal of Quantitative Spectroscopy and Radiative Transfer

Volume 15, Issue 4, April 1975, Pages 333-340

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Abstract

The intensity distribution in the rotational and vibrational structure of the CH(A²Δ − X²Π) spectrum, formed by dissociative excitation of acetylene by electron impact, is analysed. This spectrum is built-up from three overlapping bands, namely, the 0-0, 1-1 and 2-2 bands. The intensity distribution in the rotational structure of the 0-0 band is determined by an analysis of the free rotational lines of the R-branch. The intensity distribution in the other bands is analysed by a comparison of the spectrum with a spectrum simulated on the computer. In this way, the overlap of the various rotational and vibrational transitions is taken into account. It turns out that the distribution of molecules over the rotational levels can be described by assuming one Boltzmann distribution for each vibrational level.

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Emission spectra of CH(A²Δ−X²Π) produced in collisions of Ar⁺ (1.0–2.5 keV) with C₂H₂, C₂H₄ and C₂H₆ have been measured and the rovibrational distributions of CH(A²Δ) have been obtained. The rovibrational distributions of CH(A²Δ) are independent of the collision energy and agree with those produced in e-C₂H_2n(n = 1, 2, 3) collisions at electron energies of 50 eV and higher. A comparison of the present results with the previous electron-impact data suggested that the CH(A²Δ) fragments are produced through dissociation of electronically excited states of $C_{2} H_{2n}^{+∗} (n = 1, 2, 3)$ ions.
Dissociation of aliphatic hydrocarbons by controlled electron impact: Vibrational and rotational energy distributions of the excited CH radicals
1996, Chemical Physics
Emission spectra of CH(A²Δ-X²Π) produced in collisions of acetylene, ethyelen and ethane with electrons (17–100 eV) have been measured and the rovibrational distributions of CH(A²Δ) have been obtained. The rovibrational distributions of CH(A²Δ) apparently depended on the incident electron energy, indicating the existence of more than two dissociation processes. The ratio of the vibrational populations, (P(ν′ = 1)/P(ν′ = 0)), varied from 0.45, 0.3 and 0.3 at 17 eV to 0.8, 0.75 and 0.7 at 100 eV, and the rotational temperatures, T_r(ν′ = 0), varied from 3200, 5000 and 4300 K at 17 eV to 2500, 3800 and 3800 K at 100 eV for acetylene, ethylene and ethane, respectively. Component 1, which has the lowest threshold, is vibrationally cooler and rotationally hotter than components 2 and 3. The intermediate states for the formation of component 1 are σ_c-c bonding Rydberg states. The emission and formation cross sections of CHA²Δ) separated into each vibrational level were determined.
Electronic quenching of CH(A 2Δ) and NH(A 3Π) between 300 and 950 K
1995, Chemical Physics
The electronic quenching of CH(A²Δ,ν = 0) by N₂, O₂, CO₂, N₂O, and NH₃ and NH(A³Π,ν = 0) by NH₃ was investigated to extend the previously studied low temperature range towards existing high temperature data. A pulsed CO₂ laser method of rapid heating was combined with the pulsed photolytical generation of the excited species for the study of fluorescence decays in the temperature range 300 to 950 K. Together with previous literature values from Crosley's group, rate data for some systems are now available for temperatures from 240 to 1800 K. The quenching of CH(A) by N₂, CO₂ and N₂O shows a pronounced temperature dependence indicating a barrier on the reaction coordinate. Neither the united atom model nor the Parmenter-Seaver correlation nor the collision complex model reflect the temperature dependencies observed for the quenching of CH(A) by most collision partners.
Energy transfer process in the reaction of He(2 3S) with CH<inf>2</inf>Cl<inf>2</inf>
1990, Chemical Physics Letters
Energy transfer processes between metastable atoms He(2 ³S) and CH₂Cl₂ have been investigated by emission spectroscopy. Intense CH(A→X), CH(B→X), CH(C→X) and CCl(A→X) emission bands and weak hydrogen Balmer lines were observed. Using the reference reaction He(2 ³S)+CO, the formation rate constant of some fragments has been measured, i.e. k_CH(A)=8.3×10⁻¹¹ cm³ molecule⁻¹ s⁻¹, k_CH(B)=1.6×10⁻¹¹ cm³ molecule⁻¹ s⁻¹, etc. The nascent rotational temperature of CH(A ²Δ) has been estimated also.
Measurements of CH radical concentrations in an acetylene/oxygen flame and comparisons to modeling calculations
1988, Symposium (International) on Combustion
Absolute CH(X²II) and CH^*(A²) concentrations have been measured in a low pressure C₂H₂/O₂ flat flame using laser absorption and emission spectroscopy. The effect of equivalence ratio, pressure, and temperature on CH and CH^* concentrations were investigated. Both species concentrations were found to peak at approximately stoichiometric conditions and exhibited strong temperature dependences. In an 1800 K flame at 40 torr the peak CH concentration was 24 ppm while CH^* was about 1000 times less (0.018 ppm). Calculated CH concentrations using a detailed chemical kinetic mechanism and literature values for the rate constants agreed within 40 percent of the experimental measurements.
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Steady-state linear laser induced fluorescence (LIF) has been used to investigate internal energy redistribution rates in A²Δv′ = 0 CH in a low pressure oxyacetylene flame. By obtaining rotationally resolved spectra as a function of pressure the branching ratio, defined as the ratio of rotational transfer (R) out of the laser excited state divided by the electronic quenching rate (Q), was measured for a variety of flame conditions. For a stoichiometric 1600K flame and K′ = 6 excitation $R Q = 3.6 ± 0.5$ . The branching ratio was also found to increase with K′ and decrease with equivalence ratio. In addition, for K′ = 6 excitation, a value of the electronic quenching cross section of 5.4 ± 3.6 Å² was obtained.

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^∗: Present address: Philips' Research Laboratories, Eindhoven, The Netherlands.

^†: Department of Theoretical Organic Chemistry, University of Leiden, The Netherlands.

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Journal of Quantitative Spectroscopy and Radiative Transfer

Abstract

References (14)

Chem. Phys.

Comp. Phys. Comm.

Chem. Phys.

JQSRT

Physica

Thesis

J. Chem. Phys.

Cited by (24)

Dissociative excitation of aliphatic hydrocarbons (C<inf>2</inf>H<inf>2</inf>n: n = 1, 2, 3) by fast argon ion impact: Rovibrational distribution of CH(A<sup>2</sup>Δ)

Dissociation of aliphatic hydrocarbons by controlled electron impact: Vibrational and rotational energy distributions of the excited CH radicals

Electronic quenching of CH(A<sup> 2</sup>Δ) and NH(A<sup> 3</sup>Π) between 300 and 950 K

Energy transfer process in the reaction of He(2 <sup>3</sup>S) with CH<inf>2</inf>Cl<inf>2</inf>

Measurements of CH radical concentrations in an acetylene/oxygen flame and comparisons to modeling calculations

LIF study of CH A<sup>2</sup>Δ collision dynamics in a low pressure oxyacetylene flame