Rotational excitation of HOCO<sup>+</sup> by helium at low temperature

Hammami, K.; Lique, François; Jaı̈dane, N.; Lakhdar, Z. Ben; Spielfiedel, A.; Feautrier, N.

doi:10.1051/0004-6361:20066316

Cited by 21 publications

(16 citation statements)

References 22 publications

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“…This is a typical behavior of cross sections. 24,32,41 Also, our results are consistent with the same findings for HCP+ He. Note however that the values of cross sections of HCP+ para-H 2 complex are larger than those of HCP+ He in the energy interval investigated, in complete agreement with other studies reported in the literature ͑see for example Lique et al 32 ͒.…”

Section: Cross Sections and Rate Coefficientssupporting

confidence: 92%

Rotationally inelastic collisions of methinoposphide (HCP) with para-H2 at low temperature

Hammami

Nkem

Owono

et al. 2008

The Journal of Chemical Physics

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The interaction potential energy surface of the methinoposphide (HCP)-H(2) complex is calculated at the ab initio coupled-cluster level of theory with an aug-cc-pVTZ Gaussian basis set. The [H-C] and [C-P] bond lengths of HCP are set to their values at the linear equilibrium ground vibrational level of the molecule. The calculated interaction energy presents two minima located 106.3 and 67.6 cm(-1) below the HCP+H(2) dissociation limit. Using the interaction potential obtained, we have computed collision excitation cross sections in the close-coupling approach and downward rate coefficients at low temperature, i.e., T

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Section: Cross Sections and Rate Coefficientssupporting

confidence: 92%

Rotationally inelastic collisions of methinoposphide (HCP) with para-H2 at low temperature

Hammami

Nkem

Owono

et al. 2008

The Journal of Chemical Physics

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“…Equation (5) gives a first approximation of collision rate coefficients for asymmetric rotors, resulting in values within one order of magnitude of those calculated for asymmetric rotors such as SO 2 (Green 1995) and HCO + 2 (Hammami et al 2007). We, nevertheless, note that the use of this approximate formula may introduce significant errors in the excitation and abundance of NaCN.…”

Section: Molecular Datamentioning

confidence: 79%

Molecular abundances in the inner layers of IRC +10216

Agúndez

Fonfría

Cernicharo

et al. 2012

A&A

134

259

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Context. The inner layers of circumstellar envelopes around asymptotic giant branch stars are sites where a variety of processes such as thermochemical equilibrium, shocks induced by the stellar pulsation, and condensation of dust grains determine the chemical composition of the material that is expelled into the outer envelope layers and, ultimately, into interstellar space. Aims. We aim at studying the abundances, throughout the whole circumstellar envelope of the carbon star IRC +10216, of several molecules formed in the inner layers in order to constrain the different processes at work in such regions. Methods. Observations towards IRC +10216 of CS, SiO, SiS, NaCl, KCl, AlCl, AlF, and NaCN have been carried out with the IRAM 30-m telescope in the 80−357.5 GHz frequency range. A large number of rotational transitions covering a wide range of energy levels, including highly excited vibrational states, are detected in emission and serve to trace different regions of the envelope. Radiative transfer calculations based on the LVG formalism have been performed to derive molecular abundances from the innermost out to the outer layers. The excitation calculations include infrared pumping to excited vibrational states and inelastic collisions, for which up-to-date rate coefficients for rotational and, in some cases, ro-vibrational transitions are used. Results. We find that in the inner layers CS, SiO, and SiS have abundances relative to H 2 of 4 × 10 −6 , 1.8 × 10 −7 , and 3 × 10 −6 , respectively, and that CS and SiS have significant lower abundances in the outer envelope, which implies that they actively contribute to the formation of dust. Moreover, in the inner layers, the amount of sulfur and silicon in gas phase molecules is only 27% for S and 5.6% for Si, implying that these elements have already condensed onto grains, most likely in the form of MgS and SiC. Metal-bearing molecules lock up a relatively small fraction of metals, although our results indicate that NaCl, KCl, AlCl, AlF, and NaCN, despite their refractory character, are not significantly depleted in the cold outer layers. In these regions a few percent of the metals Na, K, and Al survive in the gas phase, either in atomic or molecular form, and are therefore available to participate in the gas phase chemistry in the outer envelope.

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“…The Einstein coefficients and upper level energies were retrieved from the Jet Propulsion Laboratory (JPL) database 6 (Pickett et al 1998) and the Cologne Database of Molecular Spectroscopy (CDMS) 7 (Müller et al 2001), whilst the collisional coefficients were taken from the BASECOL database 8 (Dubernet et al 2013). In particular, the references for the collisional coefficients are Flower (1999) for HCO + , Hammami et al (2007) for HOCO + , …”

Section: Physical Conditions and Abundancesmentioning

confidence: 99%

Molecular ions in the protostellar shock L1157-B1

Podio

Leflóch

Ceccarelli

et al. 2014

A&A

100

129

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Aims. We perform a complete census of molecular ions with an abundance greater than ∼10 −10 in the protostellar shock L1157-B1. This allows us to study the ionisation structure and chemistry of the shock.Methods. An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30 m and Herschel/HIFI as part of the CHESS and ASAI large programmes allows searching for molecular ions emission. Then, by means of a radiative transfer code in the large velocity gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem.Results. We detect emission from HCO + , H 13 CO + , N 2 H + , HCS + , and for the first time in a shock, from HOCO + and SO + . The bulk of the emission peaks at blue-shifted velocity, ∼0.5-3 km s −1 with respect to systemic, has a width of ∼3-7 km s −1 and is associated with the outflow cavities (T kin ∼ 20−70 K, n H 2 ∼ 10 5 cm −3 ). A high-velocity component up to −40 km s −1 , associated with the primary jet, is detected in the HCO + 1-0 line. Observed HCO + and N 2 H + abundances (X HCO + ∼ 0.7−3 × 10 −8 , X N 2 H + ∼ 0.4−8 × 10 −9 ) agree with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionisation rate ζ = 3 × 10 −16 s −1 . HOCO + , SO + , and HCS + observed abundances (X HOCO + ∼ 10 −9 , X SO + ∼ 8 × 10 −10 , X HCS + ∼ 3−7 × 10 −10 ), instead, are 1-2 orders of magnitude larger than predicted in the cloud; on the other hand, they are strongly enhanced on timescales shorter than the shock age (∼2000 years) if CO 2 , S or H 2 S, and OCS are sputtered off the dust grains in the shock. Conclusions. The performed analysis indicates that HCO + and N 2 H + are a fossil record of pre-shock gas in the outflow cavity, whilst HOCO + , SO + , and HCS + are effective shock tracers that can be used to infer the amount of CO 2 and sulphur-bearing species released from dust mantles in the shock. The observed HCS + (and CS) abundance indicates that OCS should be one of the main sulphur carrier on grain mantles. However, the OCS abundance required to fit the observations is 1-2 orders of magnitude larger than observed. Laboratory experiments are required to measure the reactions rates involving these species and to fully understand the chemistry of sulphur-bearing species.

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Rotational excitation of HOCO⁺ by helium at low temperature

Cited by 21 publications

References 22 publications

Rotationally inelastic collisions of methinoposphide (HCP) with para-H2 at low temperature

Rotationally inelastic collisions of methinoposphide (HCP) with para-H2 at low temperature

Molecular abundances in the inner layers of IRC +10216

Molecular ions in the protostellar shock L1157-B1

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Rotational excitation of HOCO+ by helium at low temperature

Cited by 21 publications

References 22 publications

Rotationally inelastic collisions of methinoposphide (HCP) with para-H2 at low temperature

Rotationally inelastic collisions of methinoposphide (HCP) with para-H2 at low temperature

Molecular abundances in the inner layers of IRC +10216

Molecular ions in the protostellar shock L1157-B1

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Rotational excitation of HOCO⁺ by helium at low temperature