Abundances of HCN and HNC in Dark Cloud Cores

Hirota, Tomoya; Yamamoto, Satoshi; Mikami, Hitomi; Ohishi, Masatoshi

doi:10.1086/306032

Cited by 246 publications

(271 citation statements)

References 43 publications

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“…From the abundance ratios of HNC, HCO + , and HCN for each IRDC in Table 4, we find that HNC is more abundant than HCO + and HCN, except for IRDC G331.035-00.418, which agree with the fact that HNC molecule is the tracer of the cold gas. And the derived NHNC/NHCN = 1.47 ± 0.50 is consistent with the results in the dark cloud cores (Hirota et al 1998). NHCN/N HCO + is approximately equal to 1, implying the similar origin and chemistry evolution of these two molecules.…”

Section: 32supporting

confidence: 88%

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A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

Liu

Wang

2013

Monthly Notices of the Royal Astronomical Society

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We have studied 14 southern infrared dark clouds (IRDCs) using the data taken from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey and the GLIMPSE and MIPSGAL mid-infrared survey of the inner Galaxy. The physical and chemical characteristics of the 14 IRDCs are investigated using N 2 H + (1-0), HNC(1-0), HCO + (1-0), and HCN(1-0) molecular lines. We find that the 14 IRDCs are in different evolutionary stages from the "starless" to the sources with an UCHII region. Three IRDCs are detected to have the star forming activities. The integrated intensity ratios I HCO + /HCN , I N2H + /HCN , and I HNC/HCN are all about 1.5, which is different from the previous measurements, suggesting that the integrated intensity ratios may be affected by the cloud environments. The integrated intensities of HNC, HCO + and HCN show a tight correlation for the 14 IRDCs, implying a close link to the chemical evolution of these three species in the IRDCs. The derived excitation temperature for each IRDC is less than 25 K. We estimate the abundances of the four molecules from 10 −11 to 10 −9 , and the average abundance ratios N HNC /N HCN = 1.47 ± 0.50, N HNC /N HCO + = 1.74 ± 0.22, N HCN /N HCO + = 1.21 ± 0.41.

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Section: 32supporting

confidence: 88%

“…N2H + was more resistant to freeze-out on grains than the carbon-bearing species (Bergin et al 2001). HNC was particularly prevalent in cold gas (Hirota et al 1998). HCO + often showed infall signatures and outflow wings (Rawlings et al 2004;Fuller et al 2005).…”

Section: Introductionmentioning

confidence: 99%

A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

Liu

Wang

2013

Monthly Notices of the Royal Astronomical Society

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“…In their study, they used the rotational excitation rate constants for HCN with He calculated by Green & Thaddeus (1974) to deduce the rate constants for the rotational excitation of HCN by H 2 , assuming that the values for HNC-He and HNC-H 2 collisions were identical to the HCN ones. (Hirota et al 1998) performed detailed HCN and HNC observations in various dense molecular clouds leading to similar results for TMC-1 to (Pratap et al 1997) despite the lower abundances derived from Hirota et al. Taking into account the various detection uncertainties, the simulated HCN abundance is compatible with a cloud age between 310 5 yr and 610 5 yr varying from (2-6)10 -8 relative to H 2 .…”

Section: Comparison With Observationsmentioning

confidence: 58%

“…(Dickens et al 2000) found higher HCN and HNC densities attributing their differences with (Swade 1989) to the optical depth estimation as Swade assumed optically thin emission, potentially underestimating the column densities. (Hirota et al 1998) were not able to evaluate the HNC abundance and therefore only reported HCN abundances. Recently (Hily-Blant et al 2010) determined CN, HCN and HNC abundances in various starless cores.…”

Section: Comparison With Observationsmentioning

confidence: 99%

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The interstellar gas-phase chemistry of HCN and HNC

Loison¹,

Wakelam²,

Hickson³

2014

Monthly Notices of the Royal Astronomical Society

104

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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Are They Linear, Bent, or Cyclic? Quantum Chemical Investigation of the Heavier Group 14 and Group 15 Homologues of HCN and HNC

Devarajan¹,

Frenking²

2012

Chemistry An Asian Journal

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The singlet potential-energy surface (PES) of the system involving the atoms H, X, and E (the (H, X, E) system) in which X=N-Bi and E=C-Pb has been explored at the CCSD(T)/TZVPP and BP86/TZ2P+ levels of theory. The nature of the X-E bonding has been analyzed with charge- and energy-partitioning methods. The calculations show that the linear isomers of the nitrogen systems lin-HEN and lin-HNE are minima on the singlet PES. The carbon compound lin-HCN (HCN=hydrogen cyanide) is 14.9 kcal mol(-1) lower in energy than lin-HNC but the heavier group 14 homologues lin-HEN (E=Si-Pb) are between 64.8 and 71.5 kcal mol(-1) less stable than the lin-HNE isomers. The phosphorous system (H, P, E) exhibits significant differences concerning the geometry and stability of the equilibrium structures compared with the nitrogen system. The linear form lin-HEP of the former system is much more stable than lin-HPE. The molecule lin-HCP is the only minimum on the singlet PES. It is 78.5 kcal mol(-1) lower in energy than lin-HPC, which is a second-order saddle point. The heavier homologues lin-HPE, in which E=Si-Pb, are also second-order saddle points, whereas the bent-HPE structures are the global minima on the PES. They are between 10.3 (E=Si) and 36.5 kcal mol(-1) (E=Pb) lower in energy than lin-HEP. The bent-HPE structures possess rather acute bending angles H-P-E between 60.1 (E=Si) and 79.7° (E=Pb). The energy differences between the heavier group 15 isomers lin-HEX (X=P-Bi) and the bent structures bent-HXE become continuously smaller. The silicon species lin-HSiBi is even 3.1 kcal mol(-1) lower in energy than bent-HBiSi. The bending angle H-X-E becomes more acute when X becomes heavier. The drastic energy differences between the isomers of the system (H, X, E) are explained with three factors that determine the relative stabilities of the energy minima: 1) The different bond strength between the hydrogen bonds H-X and H-E. 2) The electronic excitation energy of the fragment HE from the X (2)Π ground state to the (4)Σ(-) excited state, which is required to establish a E≡X triple bond in the molecules lin-HEX. 3) The strength of the intrinsic X-E interactions in the molecules. The trends of the geometries and relative energies of the linear, bent, and cyclic isomers are explained with an energy-decomposition analysis that provides deep insight into the nature of the bonding situation.

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Abundances of HCN and HNC in Dark Cloud Cores

Cited by 246 publications

References 43 publications

A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

A systemic study of 14 southern infrared dark clouds with N2H+, HNC, HCO+ and HCN lines

The interstellar gas-phase chemistry of HCN and HNC

Are They Linear, Bent, or Cyclic? Quantum Chemical Investigation of the Heavier Group 14 and Group 15 Homologues of HCN and HNC

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