Temperature dependence of the C2(X1Σg+) reaction with H2 and CH4 and C2(X1Σg+ and a 3Πu equilibrated states) with O2

Pitts, W.M.; Pasternack, Louise; McDonald, J. R.

doi:10.1016/0301-0104(82)87050-x

Cited by 72 publications

(57 citation statements)

References 21 publications

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“…Also it is reported in the literature that methane is better precursor for hard film coating compared to acetylene (Fedosenko et al, 2001). By considering all above stated facts (nature of the precursor, plasma conditions and film properties), the most probable reactions among others are calculated using the equation (19), from the known values of densities of argon, methane and electron, as well as rate constants of various processes determined from the plasma parameters and known in the literature (Alman et al, 2000;Baulch et al, 1994;Denysenko et al, 2004;Pitts et al, 1982;Shiu & Biondi, 1978;Sieck & Lias, 1976;Tsang & Hampson, 1986),…”

Section: Chemical Kineticsmentioning

confidence: 99%

Plasma-Chemical Kinetics of Film Deposition in Argon-Methane and Argon-Acetylene Mixtures Under Atmospheric Pressure Conditions

Pothiraja¹,

Bibinov²,

Awakowicz³

2012

Chemical Kinetics

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Section: Chemical Kineticsmentioning

confidence: 99%

Plasma-Chemical Kinetics of Film Deposition in Argon-Methane and Argon-Acetylene Mixtures Under Atmospheric Pressure Conditions

Pothiraja¹,

Bibinov²,

Awakowicz³

2012

Chemical Kinetics

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“…We include neutral-neutral and ion-molecule bimolecular reactions, three body processes and thermal dissociations. Important reactions involved in the build up of small organic molecules at high temperatures are those of H 2 with radicals such as C 2 and C 2 H. These reactions have been studied in the laboratory over a relatively wide temperature range: C 2 + H 2 → C 2 H + H between 295 and 493 K (Pitts et al 1982) and C 2 H + H 2 → C 2 H 2 + H in the range 178-440 K (Peeters et al 1996;Opansky & Leone 1996). They have moderate activation barriers of about 1400 K, which make them very slow in the cold interstellar medium, although at high temperatures they become rapid enough to control the abundance of C-bearing species.…”

Section: Chemical Modelmentioning

confidence: 99%

Formation of simple organic molecules in inner T Tauri disks

Agúndez¹,

Cernicharo²,

Goicoechea³

2008

A&A

155

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Aims. We present time dependent chemical models for a dense and warm O-rich gas exposed to a strong, far ultraviolet (FUV) field aimed at exploring the formation of simple organic molecules in the inner regions of protoplanetary disks around T Tauri stars.Methods. An up-to-date chemical network is used to compute the evolution of molecular abundances. Reactions of H 2 with small organic radicals such as C 2 and C 2 H, which are not included in current astrochemical databases, overcome their moderate activation energies at warm temperatures and become very important for the gas phase synthesis of C-bearing molecules.Results. The photodissociation of CO and release of C triggers the formation of simple organic species such as C 2 H 2 , HCN, and CH 4 . In timescales between 1 and 10 4 years, depending on the density and FUV field, a steady state is reached in the model in which molecules are continuously photodissociated, but also formed, mainly through gas phase chemical reactions involving H 2 . Conclusions. The application of the model to the upper layers of inner protoplanetary disks predicts large gas phase abundances of C 2 H 2 and HCN. The implied vertical column densities are as large as several 10 16 cm −2 in the very inner disk (<1 AU), in good agreement with the recent infrared observations of warm C 2 H 2 and HCN in the inner regions of IRS 46 and GV Tau disks. We also compare our results with previous chemical models studying the photoprocessing in the outer disk regions, and find that the gas phase chemical composition in the upper layers of the inner terrestrial zone (a few AU) is predicted to be substantially different from that in the upper layers of the outer disk (>50 AU).

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“…Figure 18 shows that most small hydrocarbons show a first abundance peak near the illuminated edge of the cloud where the predicted gas temperature sharply goes from ∼1000 K in the cloud surface, close to the ionisation front, to ∼150 K near the dissociation front at A V ≈ 1.5. Such elevated temperatures contribute to enhancing the abundance of C 2 H through the C 2 + H 2 → C 2 H + H reaction, which has an activation energy barrier of E/k ≈ 1500 K (Pitts et al 1982). For the physical conditions prevailing in the edge of Orion Bar, this neutral-neutral reaction dominates the gas-phase formation of abundant C 2 H. For this reason, the gas-phase production of C 2 H may be more efficient in dense and hot PDRs than in cool PDRs (we note the higher peak C 2 H abundance in the clump model compared to the interclump model in Fig.…”

Section: Pdr Models Of the Orion Barmentioning

confidence: 99%

The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR

Cuadrado

Goicoechea

Pilleri

et al. 2015

A&A

123

177

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Context. Carbon chemistry plays a pivotal role in the interstellar medium (ISM) but even the synthesis of the simplest hydrocarbons and how they relate to polycyclic aromatic hydrocarbons (PAHs) and grains is not well understood. Aims. We study the spatial distribution and chemistry of small hydrocarbons in the Orion Bar photodissociation region (PDR), a prototypical environment in which to investigate molecular gas irradiated by strong UV fields. Methods. We used the IRAM 30 m telescope to carry out a millimetre line survey towards the Orion Bar edge, complemented with ∼2 × 2 maps of the C 2 H and c-C 3 H 2 emission. We analyse the excitation of the detected hydrocarbons and constrain the physical conditions of the emitting regions with non-LTE radiative transfer models. We compare the inferred column densities with updated gas-phase photochemical models including 13 CCH and C 13 CH isotopomer fractionation.Results. Approximately 40% of the lines in the survey arise from hydrocarbons (C 2 H, C 4 H, c-C 3 H 2 , c-C 3 H, C 13 CH, 13 CCH, l-C 3 H, and l-H 2 C 3 in decreasing order of abundance). We detect new lines from l-C 3 H + and improve its rotational spectroscopic constants. Anions or deuterated hydrocarbons are not detected, but we provide accurate upper limit abundances:Conclusions. Our models can reasonably match the observed column densities of most hydrocarbons (within factors of <3). Since the observed spatial distribution of the C 2 H and c-C 3 H 2 emission is similar but does not follow the PAH emission, we conclude that, in high UV-flux PDRs, photodestruction of PAHs is not a necessary requirement to explain the observed abundances of the smallest hydrocarbons. Instead, gas-phase endothermic reactions (or with barriers) between C + , radicals, and H 2 enhance the formation of simple hydrocarbons. Observations and models suggest that the [C 2 H]/[c-C 3 H 2 ] ratio (∼32 at the PDR edge) decreases with the UV field attenuation. The observed low cyclic-to-linear C 3 H column density ratio (≤3) is consistent with a high electron abundance (x e ) PDR environment. In fact, the poorly constrained x e gradient influences much of the hydrocarbon chemistry in the more UV-shielded gas. The inferred hot rotational temperatures for C 4 H and l-C 3 H + also suggest that radiative IR pumping affects their excitation. We propose that reactions of C 2 H isotopologues with 13 C + and H atoms can explain the observed [C 13 CH]/[ 13 CCH] = 1.4 ± 0.1 fractionation level.

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Temperature dependence of the C2(X1Σg+) reaction with H2 and CH4 and C2(X1Σg+ and a 3Πu equilibrated states) with O2

Cited by 72 publications

References 21 publications

Plasma-Chemical Kinetics of Film Deposition in Argon-Methane and Argon-Acetylene Mixtures Under Atmospheric Pressure Conditions

Plasma-Chemical Kinetics of Film Deposition in Argon-Methane and Argon-Acetylene Mixtures Under Atmospheric Pressure Conditions

Formation of simple organic molecules in inner T Tauri disks

The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR

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