Laboratory measurements of the abundance ratio (HCO+)/((HOC+) and their astrophysical implications

Amano, Tatsuya; Nakanaga, Taisuke

doi:10.1086/166299

Cited by 9 publications

(11 citation statements)

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“…The formyl cation was astronomically detected in 1970 and has been the subject of many investigations, mainly due to its isomeric character. − Formyl (HCO + ) and isoformyl (HOC + ) cations are supposed to initiate different interstellar chemical channels, so that a deep understanding of their interplay and relative abundance is of fundamental relevance in order to model accurate chemical networks. In the last decades, many astronomical observations have obtained vastly different HCO + /HOC + ratios between about 360 to 6000, thereby demonstrating a strong dependence of the relative isomer abundances on the specific chemical composition and evolution of the monitored region. − …”

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confidence: 99%

Preferential Isomer Formation Observed in H₃⁺ + CO by Crossed Beam Imaging

Carrascosa

Kainz

Stei

et al. 2016

J. Phys. Chem. Lett.

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The proton transfer reaction H3+ + CO is one of the cornerstone chemical processes in the interstellar medium. Here, the dynamics of this reaction have been investigated using crossed beam velocity map imaging. Formyl product cations are found to be predominantly scattered into the forward direction irrespective of the collision energy. In this process, a high amount of energy is transferred to internal product excitation. By fitting a sum of two distribution functions to the measured internal energy distributions, the product isomer ratio is extracted. A small HOC+ fraction is obtained at a collision energy of 1.8 eV, characterized by an upper limit of 24% with a confidence level of 84%. At lower collision energies, the data indicate purely HCO+ formation. Such low values are unexpected given the previously predicted efficient formation of both HCO+ and HOC+ isomers for thermal conditions. This is discussed in light of the direct reaction dynamics that are observed.

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confidence: 99%

Preferential Isomer Formation Observed in H₃⁺ + CO by Crossed Beam Imaging

Carrascosa

Kainz

Stei

et al. 2016

J. Phys. Chem. Lett.

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“…The formation enthalpies for these two isomers are Δ H f (ion) = 825.6 kJ/mol for HCO + and Δ H f (ion) = 963–990 kJ/mol for HOC + , respectively. , The difference in formation enthalpies of 1.42–1.70 eV obtained from these figures is of the same order as other reported values of 1.63–1.72 eV, whereas the classical barrier height for proton migration and proton exchange with CO has been found to be ∼1.5–3.3 eV at 0 K. ,, The lower formation enthalpy for HCO + should increase the probability of forming this isomer in the ion source. Geppert et al argued in an earlier article that the conditions in the ion source should be similar to those in a hollow cathode discharge experiment by Amano and Nagakana who reported a maximum yield for the HOC + isomer of 2%. In this study, fractions of HCO + /HOC + were measured with optical spectroscopic methods as a function of the CO and H 2 pressures …”

Section: Resultsmentioning

confidence: 94%

“…Geppert et al argued in an earlier article that the conditions in the ion source should be similar to those in a hollow cathode discharge experiment by Amano and Nagakana who reported a maximum yield for the HOC + isomer of 2%. In this study, fractions of HCO + /HOC + were measured with optical spectroscopic methods as a function of the CO and H 2 pressures …”

Section: Resultsmentioning

confidence: 94%

“…It is worth noting, however, that other methods of ion creation have reported different levels of HOC + fractionation. Formation of the ion by protonation of CO with H 3 + has yielded HOC + fractions of up to 6%, which were determined by collision-induced dissociation (CID). , However, it is arguable that uncertainties inherent in such CID measurements should be larger compared with those obtained through the spectroscopic methods used by Amano and Nakanaga . The HOC + branching fraction for production of HCO + by reactions of CO + with H 2 and C + with H 2 O has been found to be as large as 48% and 84%, respectively, in selected-ion flow tube (SIFT) measurements .…”

Section: Resultsmentioning

confidence: 99%

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Experimental Studies of H¹³CO⁺ Recombining with Electrons at Energies between 2–50 000 meV

et al. 2014

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An investigation into the dissociative recombination process for H(13)CO(+) using merged ion-electron beam methods has been performed at the heavy ion storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions of the different product channels at ∼ 0 eV collision energy to be the following: CO + H 87 ± 2%, OH + C 9 ± 2%, and O + CH 4 ± 2%. The formation of electronically excited CO in the dominant reaction channel has also been studied, and we report the following tentative branching fractions for the different CO product electronic states: CO(X (1)Σ(+)) + H, 54 ± 10%; CO(a (3)Π) + H, 23 ± 4%; and CO(a' (3)Σ(+)) + H, 23 ± 4%. The absolute cross section between ∼ 2-50 000 meV was measured and showed resonance structures between 3 and 15 eV. The cross section was fitted in the energy range relevant to astrophysics, i.e., between 1 and 300 meV, and was found to follow the expression σ = 1.3 ± 0.3 × 10(-16) E(-1.29 ± 0.05) cm(2) and the corresponding thermal rate constant was determined to be k(T) = 2.0 ± 0.4 × 10(-7)(T/300)(-0.79 ± 0.05) cm(3) s(-1). Radioastronomical observations with the IRAM 30 m telescope of HCO(+) toward the Red Rectangle yielded an upper column density limit of 4 × 10(11) cm(-2) of HCO(+) at the 1σ level in that object, indicating that previous claims that the dissociative recombination of HCO(+) plays an important role in the production of excited CO molecules emitting the observed Cameron bands in that object are not supported.

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“…Also the metastable isoformyl cation HOC + is formed in this reaction and has been observed in dense molecular clouds [6,7]. The HCO + /HOC + branching ratio in different environments and future detections are subject to ongoing interest [8][9][10][11] and comparison to models suggests that HOC + must be considered in reliable abundance calculations [12]. Also the rapid HOC + to HCO + conversion by H 2 was subject to a controversial discussion [9,13].…”

Section: Introductionmentioning

confidence: 99%