Theoretical Elucidation of the Unusually High [HNC]/[HCN] Abundance Ratio in Interstellar Space: Two‐dimensional and Two‐State Quantum Wave Packet Dynamics Study on the Branching Ratio of the Dissociative Recombination Reaction HCNH++e−→ HNC/HCN + H

Ishii, Katsuya; Tajima, Asami; Taketsugu, Tetsuya; Yamashita, Koichi

doi:10.1086/498343

Cited by 28 publications

(17 citation statements)

References 23 publications

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“…There are various theoretical studies of the DR reaction of HCNH + leading to similar results despite disagreement for the mechanism which involves either a direct formation pathway (Talbi & Ellinger 1998, Hickman et al 2005 or an indirect process (Shiba et al 1998, Taketsugu et al 2004, Ishii et al 2006 as these authors found no possibility for the direct process. However all studies of the direct and indirect processes lead to similar branching ratios for HCN and HNC formation.…”

Section: Resultsmentioning

confidence: 79%

The interstellar gas-phase chemistry of HCN and HNC

Loison¹,

Wakelam²,

Hickson³

2014

Monthly Notices of the Royal Astronomical Society

108

109

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+ CH 2 reaction and two new reactions: H + CCN and C + HNC. We test the effect of the new rate constants and branching ratios on the predictions of gas-grain chemical models for dark cloud conditions. The rapid C + HNC reaction keeps the HCN/HNC ratio significantly above one as long as the carbon atom abundance remains high. However, the reaction of HCN with H 3 + followed by DR of HCNH + acts to isomerize HCN into HNC when carbon atoms and CO are depleted leading to a HCN/HNC ratio close to or slightly greater than 1. This agrees well with observations in TMC-1 and L134N taking into consideration the overestimation of HNC abundances through the use of the same rotational excitation rate constants for HNC as for HCN in many radiative transfer models.

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Section: Resultsmentioning

confidence: 79%

The interstellar gas-phase chemistry of HCN and HNC

Loison¹,

Wakelam²,

Hickson³

2014

Monthly Notices of the Royal Astronomical Society

108

109

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“…The theoretical results presented in Talbi & Herbst (1998) and Herbst et al (2000), and more recently by Hickman et al (2005) and Ishii et al (2006), show quite convincingly that the HNC/HCN abundance ratio resulting from the chemical reactions known to be effective in dark clouds cannot differ significantly from unity. There are two possible explanations for the discrepancy between the observations and theoretical predictions.…”

Section: The Chemical State Of Cha-mms1 and The Hnc/hcnmentioning

confidence: 76%

“…Recent theoretical studies corroborate Based on observations collected at the European Southern Observatory, La Silla, Chile, and at the Parkes Observatory operated by the Australia Telescope National Facility (ATNF). the equal branching ratios for HCN and HNC in dissociative recombination (Hickman et al 2005;Ishii et al 2006). HNC/HCN column density ratios clearly larger than unity have been reported: Churchwell et al 1984 find that [HNC]/[HCN] may be as high as ∼10 in some dark clouds cores, and Hirota et al (1998) find a ratio of ∼5 in L1498.…”

Section: Introductionmentioning

confidence: 99%

HCN and HNC mapping of the protostellar core Chamaeleon-MMS1

Tennekes

Harju²,

Juvela³

et al. 2006

A&A

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Aims. The purpose of this study is to investigate the distributions of the isomeric molecules HCN and HNC and estimate their abundance ratio in the protostellar core Cha-MMS1 located in Chamaeleon i.Methods. The core was mapped in the J = 1−0 rotational lines of HCN, HNC, and HN 13 C. The column densities of H 13 CN, HN 13 C, H 15 NC and NH 3 were estimated towards the centre of the core. Results. The core is well delineated in all three maps. The kinetic temperature in the core, derived from the NH 3 (1, 1) and (2, 2) inversion lines, is 12.1 ± 0.1 K. The HN 13 C/H 13 CN column density ratio is between 3 and 4, i.e. similar to values found in several other cold cores. The HN 13 C/H 15 NC column density ratio is ∼7. In case no 15 N fractionation occurs in HNC (as suggested by recent modelling results), the HNC/HN 13 C abundance ratio is in the range 30−40, which indicates a high degree of 13 C fractionation in HNC. Assuming no differential 13 C fractionation the HCN and HNC abundances are estimated to be ∼7 × 10 −10 and ∼2 × 10 −9 , respectively, the former being nearly two orders of magnitude smaller than that of NH 3 . Using also previously determined column densities in Cha-MMS1, we can put the most commonly observed nitrogenous molecules in the following order according to their fractional abundances: χ(NH 3 ) > χ(HC 3 N) > χ(HNC) > χ(HCN) > χ(N 2 H + ). Conclusions. The relationships between molecular abundances suggest that Cha-MMS1 represents an evolved chemical stage, experiencing at present the "late-time" cyanopolyyne peak. The possibility that the relatively high HNC/HCN ratio derived here is only valid for the 13 C isotopic substitutes cannot be excluded on the basis of the present and other available data.

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“…Although no such experiments have been performed on HNC, the results obtained for HCN provide relevant information also for the highly excited vibrational states of HNC. Hirano et al [9,12] and also Ishii et al [13] found theoretically that the neutral products HCN and HNC are formed in their ground electronic states after the dissociative recombination. The majority of the internal energy would be carried away as the vibrational energy.…”

Section: Discussionmentioning

confidence: 94%

“…A direct trajectory simulation for the dissociative recombination reaction at the Hartree-Fock level was made by Tachikawa [11]. Extensive ab initio dynamics calculations were carried out to elucidate the details of the reaction processes and the branching ratio of 1 was obtained [12,13]. On the other hand, Talbi and Ellinger [14] and more recently Hickman et al [15] proposed a direct dissociative recombination mechanism.…”

Section: Introductionmentioning

confidence: 99%