Hydrocarbon Anions in Interstellar Clouds and Circumstellar Envelopes

Millar, T. J.; Walsh, Catherine; Cordiner, Martin; Chuimin, Roisin Ni; Herbst, Eric

doi:10.1086/519376

Cited by 101 publications

(154 citation statements)

References 21 publications

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“…comm.). We have also recalculated anion photorates using the Draine interstellar radiation field (Draine 1978), and the power law described in Millar et al (2007). Rate12 now includes at least one photoprocess for every neutral species in the reaction network.…”

Section: Photoprocessesmentioning

confidence: 99%

“…Bruhns et al (2010), Brunetti & Liuti (1975) Harada & Herbst (2008), Harrison et al (1986), Hasegawa & Herbst (1993), Hawley et al (1990), Hemsworth et al (1974), Herbst (1983), Herbst et al (1984), Herbst & Leung (1986), Herbst et al (1989a), Herbst & Leung (1989), Herbst et al (1989b), Herbst et al (1989c), Herbst & Leung (1990), Herbst et al (2000), Herbst & Osamura (2008), Herbst et al (2010), Herrero et al (2010), Hoobler & Leone (1997), Huo et al (2011), Iglesias (1977, Inomata & Washida (1999), Johnson et al (2000), , Kalhori et al (2002), Kamińska et al (2008), Kern et al (1988), Wakelam et al (2012), Klippenstein et al (2010), Kuan et al (1999) Millar et al (1985), Millar et al (1986), Millar et al (1987), Millar et al (1988), Millar & Herbst (1990), Millar (1991, Millar et al (1991), Millar et al (1997b), Millar et al (2000), Millar et al (2007), Mi...…”

Section: Appendix A: Rate12 Referencesmentioning

confidence: 99%

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The UMIST database for astrochemistry 2012

McElroy

Walsh

Markwick

et al. 2013

A&A

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858

880

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We present the fifth release of the UMIST Database for Astrochemistry (UDfA). The new reaction network contains 6173 gas-phase reactions, involving 467 species, 47 of which are new to this release. We have updated rate coefficients across all reaction types. We have included 1171 new anion reactions and updated and reviewed all photorates. In addition to the usual reaction network, we also now include, for download, state-specific deuterated rate coefficients, deuterium exchange reactions and a list of surface binding energies for many neutral species. Where possible, we have referenced the original source of all new and existing data. We have tested the main reaction network using a dark cloud model and a carbon-rich circumstellar envelope model. We present and briefly discuss the results of these models.

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Section: Photoprocessesmentioning

confidence: 99%

Section: Appendix A: Rate12 Referencesmentioning

confidence: 99%

The UMIST database for astrochemistry 2012

McElroy

Walsh

Markwick

et al. 2013

A&A

Self Cite

858

880

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“…If it happens that the autodetachment width of this new state is small or the probability of the spontaneous emission for this state is enhanced, for example, due to a better Franck-Condon overlap, one can expect that the system will not be able to loose rapidly the attached electron and will eventually be stabilized by emitting a photon. If this happens, then the IREA cross section (16) should be modified as…”

Section: Competition Between Radiative Stabilization and Autodetacmentioning

confidence: 99%

“…The theoretical approach proposed by Herbst, the phase-space theory (PST), has been used in a number of studies [3,[12][13][14][15][16][17] to calculate the REA rate coefficients and to model formation of anions in the ISM. The approach has been successful in interpreting the observed column density of C 8 H − , C 6 H − , C 5 N − and C 3 N − ions, while the agreement with observations is not as good for the C 4 H − and CN − ions.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of radiative electron attachment to CN, C2H, and C4H radicals

Douguet

Santos

Raoult

et al. 2015

The Journal of Chemical Physics

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A first-principle theoretical approach to study the process of radiative electron attachment is developed and applied to the negative molecular ions CN − , C4H − , and C2H − . Among these anions, the first two have already been observed in the interstellar space. Cross sections and rate coefficients for formation of these ions by radiative electron attachment to the corresponding neutral radicals are calculated. For completeness of the theoretical approach, two pathways for the process have been considered: (i) A direct pathway, in which the electron in collision with the molecule spontaneously emits a photon and forms a negative ion in one of the lowest vibrational levels, and (ii) an indirect, or two-step pathway, in which the electron is initially captured through non-BornOppenheimer coupling into a vibrationally resonant excited state of the anion, which then stabilizes by radiative decay. We develop a general model to describe the second pathway and show that its contribution to the formation of cosmic anions is small in comparison to the direct mechanism. The obtained rate coefficients at 30 K are 7 × 10 −16 cm 3 /s for CN − , 7 × 10 −17 cm 3 /s for C2H − , and 2 × 10 −16 cm 3 /s for C4H − . These rates weakly depend on temperature between 10K and 100 K. The validity of our calculations is verified by comparing the present theoretical results with data from recent photodetachment experiments.

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“…However, this same process results in a veritable sea of elections that could attach to neutrals and actually lead to the creation of anions even in the Horsehead nebula PDR (Millar et al 2007). Additionally, many anions are known to be surprisingly stable (Hammer et al 2003;Simons 2008Simons , 2011Fortenberry & Crawford 2011b, 2011aFortenberry 2013), and electron attachment rates are also believed to be quite high in these regions (Millar et al 2007). Several anions have also been shown to possess dipolebound excited states, or threshold resonances, which may play a significant role in the creation and recreation of interstellar anions (Güthe et al 2001;Carelli et al 2013).…”

Section: Astrochemical Considerationsmentioning

confidence: 99%

HIGH-ACCURACY QUARTIC FORCE FIELD CALCULATIONS FOR THE SPECTROSCOPIC CONSTANTS AND VIBRATIONAL FREQUENCIES OF 1¹A′l-C₃H^–: A POSSIBLE LINK TO LINES OBSERVED IN THE HORSEHEAD NEBULA PHOTODISSOCIATION REGION

Fortenberry

Huang

Crawford

et al. 2013

ApJ

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It has been shown that rotational lines observed in the Horsehead nebula photodissociation region (PDR) are probably not caused by l-C 3 H + , as was originally suggested. In the search for viable alternative candidate carriers, quartic force fields are employed here to provide highly accurate rotational constants, as well as fundamental vibrational frequencies, for another candidate carrier: 1 1 A C 3 H − . The ab initio computed spectroscopic constants provided in this work are, compared to those necessary to define the observed lines, as accurate as the computed spectroscopic constants for many of the known interstellar anions. Additionally, the computed D eff for C 3 H − is three times closer to the D deduced from the observed Horsehead nebula lines relative to l-C 3 H + . As a result, 1 1 A C 3 H − is a more viable candidate for these observed rotational transitions. It has been previously proposed that at least C 6 H − may be present in the Horsehead nebular PDR formed by way of radiative attachment through its dipole-bound excited state. C 3 H − could form in a similar way through its dipole-bound state, but its valence excited state increases the number of relaxation pathways possible to reach the ground electronic state. In turn, the rate of formation for C 3 H − could be greater than the rate of its destruction. C 3 H − would be the seventh confirmed interstellar anion detected within the past decade and the first C n H − molecular anion with an odd n.

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Hydrocarbon Anions in Interstellar Clouds and Circumstellar Envelopes

Cited by 101 publications

References 21 publications

The UMIST database for astrochemistry 2012

The UMIST database for astrochemistry 2012

Theoretical study of radiative electron attachment to CN, C2H, and C4H radicals

HIGH-ACCURACY QUARTIC FORCE FIELD CALCULATIONS FOR THE SPECTROSCOPIC CONSTANTS AND VIBRATIONAL FREQUENCIES OF 1¹A′l-C₃H^–: A POSSIBLE LINK TO LINES OBSERVED IN THE HORSEHEAD NEBULA PHOTODISSOCIATION REGION

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Hydrocarbon Anions in Interstellar Clouds and Circumstellar Envelopes

Cited by 101 publications

References 21 publications

The UMIST database for astrochemistry 2012

The UMIST database for astrochemistry 2012

Theoretical study of radiative electron attachment to CN, C2H, and C4H radicals

HIGH-ACCURACY QUARTIC FORCE FIELD CALCULATIONS FOR THE SPECTROSCOPIC CONSTANTS AND VIBRATIONAL FREQUENCIES OF 11A′l-C3H–: A POSSIBLE LINK TO LINES OBSERVED IN THE HORSEHEAD NEBULA PHOTODISSOCIATION REGION

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HIGH-ACCURACY QUARTIC FORCE FIELD CALCULATIONS FOR THE SPECTROSCOPIC CONSTANTS AND VIBRATIONAL FREQUENCIES OF 1¹A′l-C₃H^–: A POSSIBLE LINK TO LINES OBSERVED IN THE HORSEHEAD NEBULA PHOTODISSOCIATION REGION