Rotational excitation and de-excitation of CH<sup>+</sup>molecules by<sup>4</sup>He atoms

Turpin, F.; Stoecklin, Thierry; Voronin, A. I.

doi:10.1051/0004-6361/200912744

Cited by 17 publications

(13 citation statements)

References 22 publications

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“…In the following we consider both H 2 and electron collisions to probe the excitation of CH + and SH + . For CH + our calculations are based on collision rates from Turpin et al (2010), for temperatures in the range between 10 K and 200 K, covering transitions up to the 5-4 transition (E up = 599.5 K). These rates have been scaled from CH + −He to CH + −H 2 based on Schöier et al (2005).…”

Section: Physical Conditions Traced By Ch + and Sh +mentioning

confidence: 99%

The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

Nagy

Tak

Ossenkopf

et al. 2013

A&A

203

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Context. The abundances of interstellar CH + and SH + are not well understood as their most likely formation channels are highly endothermic. Several mechanisms have been proposed to overcome the high activation barriers, including shocks, turbulence, and H 2 vibrational excitation. Aims. Using data from the Herschel Space Observatory, we studied the formation of ions, in particular CH + and SH + in a typical high UV-illumination warm and dense photon-dominated region (PDR), the Orion Bar. Methods. The HIFI instrument on board Herschel provides velocity-resolved line profiles of CH + 1-0 and 2-1 and three hyperfine transitions of SH + 1 2 −0 1 . The PACS instrument provides information on the excitation and spatial distribution of CH + by extending the observed CH + transitions up to J = 6-5. We compared the observed line intensities to the predictions of radiative transfer and PDR codes. Results. All CH + , SH + , and CF + lines analyzed in this paper are seen in emission. The widths of the CH + 2-1 and 1-0 transitions are of ∼5 km s −1 , significantly broader than the typical width of dense gas tracers in the Orion Bar (∼2-3 km s −1 ) and are comparable to the width of species that trace the interclump medium such as C + and HF. The detected SH + transitions are narrower compared to CH + and have line widths of ∼3 km s −1 , indicating that SH + emission mainly originates in denser condensations. Non-LTE radiative transfer models show that electron collisions affect the excitation of CH + and SH + and that reactive collisions need to be taken into account to calculate the excitation of CH + . Comparison to PDR models shows that CH + and SH + are tracers of the warm surface region (A V < 1.5) of the PDR with temperatures between 500 and 1000 K. We have also detected the 5-4 transition of CF + at a width of ∼1.9 km s −1 , consistent with the width of dense gas tracers. The intensity of the CF + 5-4 transition is consistent with previous observations of lower-J transitions toward the Orion Bar.Conclusions. An analytic approximation and a numerical comparison to PDR models indicate that the internal vibrational energy of H 2 can explain the formation of CH + for typical physical conditions in the Orion Bar near the ionization front. The formation of SH + is also likely to be explained by H 2 vibrational excitation. The abundance ratios of CH + and SH + trace the destruction paths of these ions, and indirectly, the ratios of H, H 2 , and electron abundances as a function of depth into the cloud.

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Section: Physical Conditions Traced By Ch + and Sh +mentioning

confidence: 99%

The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

Nagy

Tak

Ossenkopf

et al. 2013

A&A

203

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“…The most complete model is that of Godard & Cernicharo (2013) which includes the radiative pumping of CH + vibrational and electronic states by infrared, optical and ultraviolet photons. In all these studies, inelastic data were taken from the state-to-state calculations of Hammami, Owono Owono & Stäuber (2009) and Turpin, Stoecklin & Voronin (2010) on CH + -He and those of Lim, Rabadán & Tennyson (1999) on CH + -electron, and they were complemented by extrapolations. For the destruction by reactions with H, electrons and H 2 , generic rates independent of j were assumed, except for CH + + H in Godard & Cernicharo (2013) where the initial-state-specific rate coefficients extracted by Plasil et al (2011) for j = 0, 1, 2 at T k ≤ 60 K were used.…”

Section: Introductionmentioning

confidence: 99%

State-to-state chemistry and rotational excitation of CH+ in photon-dominated regions

Fauré

Halvick

Stoecklin

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a detailed theoretical study of the rotational excitation of CH + due to reactive and nonreactive collisions involving C + ( 2 P), H 2 , CH + , H and free electrons. Specifically, the formation of CH + proceeds through the reaction between C + ( 2 P) and H 2 (ν H 2 = 1, 2), while the collisional (de)excitation and destruction of CH + is due to collisions with hydrogen atoms and free electrons. State-to-state and initial-state-specific rate coefficients are computed in the kinetic temperature range 10-3000 K for the inelastic, exchange, abstraction and dissociative recombination processes using accurate potential energy surfaces and the best scattering methods. Good agreement, within a factor of 2, is found between the experimental and theoretical thermal rate coefficients, except for the reaction of CH + with H atoms at kinetic temperatures below 50 K. The full set of collisional and chemical data are then implemented in a radiative transfer model. Our Non-LTE calculations confirm that the formation pumping due to vibrationally excited H 2 has a substantial effect on the excitation of CH + in photon-dominated regions. In addition, we are able to reproduce, ⋆ alexandre.faure@univ-grenoble-alpes.fr. Europe PMC Funders GroupAuthor Manuscript Mon Not R Astron Soc. Author manuscript; available in PMC 2017 July 06. Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts within error bars, the far-infrared observations of CH + toward the Orion Bar and the planetary nebula NGC 7027. Our results further suggest that the population of ν H 2 = 2 might be significant in the photon-dominated region of NGC 7027.

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“…(1) Jaquet et al (1992); (2) Abrahamsson et al (2007); (3) Schöier et al (2005); (4) Bell et al (1998); (5) Wilson & Bell (2002); (6) Hammami et al (2009);Turpin et al (2010), rates for He scaled by 1.39; (7) Lim et al (1999); (8) Flower (1999); (9) Yang et al (2010); (10) Balakrishnan et al (2002); (11) Cecchi-Pestellini et al (2002); (12) Offer et al (1994); (13) Green (1980); (14) Faure & Josselin (2008).…”

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Uncertainties in water chemistry in disks: An application to TW Hydrae

Kamp¹,

Thi

Meeus

et al. 2013

A&A

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Context. This paper discusses the sensitivity of water lines to chemical processes and radiative transfer for the protoplanetary disk around TW Hya. The study focuses on the Herschel spectral range in the context of new line detections with the PACS instrument from the Gas in Protoplanetary Systems project (GASPS). Aims. The paper presents an overview of the chemistry in the main water reservoirs in the disk around TW Hya. It discusses the limitations in the interpretation of observed water line fluxes. Methods. We use a previously published thermo-chemical Protoplanetary Disk Model (ProDiMo) of the disk around TW Hya and study a range of chemical modeling uncertainties: metallicity, C/O ratio, and reaction pathways and rates leading to the formation of water. We provide results for the simplified assumption of T gas = T dust to quantify uncertainties arising for the complex heating/cooling processes of the gas and elaborate on limitations due to water line radiative transfer. Conclusions. Due to their sensitivity on chemical input data and radiative transfer, water lines have to be used cautiously for understanding details of the disk structure. Water lines covering a wide range of excitation energies provide access to the various gas phase water reservoirs (inside and outside the snow line) in protoplanetary disks and thus provide important information on where gas-phase water is potentially located. Experimental and/or theoretical collision rates for H 2 O with atomic hydrogen are needed to diminish uncertainties from water line radiative transfer.

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Rotational excitation and de-excitation of CH⁺molecules by⁴He atoms

Cited by 17 publications

References 22 publications

The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

State-to-state chemistry and rotational excitation of CH+ in photon-dominated regions

Uncertainties in water chemistry in disks: An application to TW Hydrae

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Rotational excitation and de-excitation of CH+molecules by4He atoms

Cited by 17 publications

References 22 publications

The chemistry of ions in the Orion Bar I. – CH+, SH+, and CF+

The chemistry of ions in the Orion Bar I. – CH+, SH+, and CF+

State-to-state chemistry and rotational excitation of CH+ in photon-dominated regions

Uncertainties in water chemistry in disks: An application to TW Hydrae

Contact Info

Product

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Rotational excitation and de-excitation of CH⁺molecules by⁴He atoms

The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺