Rotational excitation of aluminium monofluoride (AlF) by He atom at low temperature

Gotoum, Nadjinangar; Nkem, C.; Hammami, K.; Charfadine, M. Ahamat; Owono, L. C. Owono; Jaı̈dane, N.

doi:10.1007/s10509-010-0495-7

Cited by 19 publications

(10 citation statements)

References 32 publications

(33 reference statements)

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“…Also, the excitation temperature of AlF derived here is consistent with the kinetic temperature constrained from the single-dish survey (12). Using collision rates of AlF with p-H 2 and with He at 10 K (39,40), we calculated critical densities for all observed transitions. They range from 10 4 cm -3 for J=1-0 to 10 7 cm -3 for J=7-6 and are therefore comparable to critical densities of analogous transitions of low-density molecular tracers such as CO.…”

Section: Spectroscopic Data For Alf Isotopologuessupporting

confidence: 74%

Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

et al. 2018

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Decades ago, γ-ray observatories identified diffuse Galactic emission at 1.809 MeV (1-3) originating from β + decays of an isotope of aluminium, 26 Al, that has a mean-life time of 1.04 million years (4). Objects responsible for the production of this radioactive isotope have never been directly identified, owing to insufficient angular resolutions and sensitivities of the γ-ray observatories. Here, we report observations of millimetre-wave rotational lines of the isotopologue of aluminium monofluoride that contains the radioactive isotope ( 26 AlF). The emission is observed toward CK Vul which is thought to be a remnant of a stellar merger (5-7). Our constraints on the production of 26 Al combined with the estimates on the merger rate make it unlikely that objects similar to CK Vul are major producers of Galactic 26 Al. However, the observation may be a stepping stone for unambiguous identification of other Galactic sources of 26 Al. Moreover, a high content of 26

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Section: Spectroscopic Data For Alf Isotopologuessupporting

confidence: 74%

Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

et al. 2018

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“…We have not included vibrationally excited states since no lines involving such states are observed in IRC +10216, and since vibrational line strengths for those molecules are poorly known. Recently, Gotoum et al (2011Gotoum et al ( , 2012 have calculated the rate coefficients for AlF de-excitation through collisions with He and para H 2 up to temperatures of 300 and 70 K, respectively. We have also used those rate coefficients for AlCl, which has a similar dipole moment than AlF.…”

Section: Molecular Datamentioning

confidence: 99%

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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“…In interstellar molecular clouds, the most abundant element hydrogen is predominantly in the form of H 2 molecules and therefore one has to account for the collisions between H 2 CSi and H 2 molecules. For convenience, H 2 is considered as structureless and is replaced by the He atom (Machin and Roueff 2007, Rabli and Flower 2010, Gotoum et al 2011, Spielfiedel et al 2012, Sharma et al 2014b, 2014c as both the He and H 2 have two protons and two electrons, and the interaction potential depends on charges of the colliding particles.…”

Section: Collisional Rate Coefficientsmentioning

confidence: 99%

Radiative transfer in silylidene molecule

2014

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In order to search for silylidene (H 2 CSi) in the interstellar medium, Izuha et al. (1996) recorded microwave spectrum of H 2 CSi in laboratory and made an unsuccessful attempt of its identification in IRC +10216, Ori KL, Sgr B2, through its 7 17 − 6 16 transition at 222.055 GHz. For finding out if there are other transitions of H 2 CSi which may help in its identification in the interstellar medium, we have considered 25 rotational levels of ortho-H 2 CSi connected by collisional transitions and 35 radiative transitions, and solved radiative transfer problem using the LVG approximation. We have found that the brightness temperatures of 9 transitions are larger than that of 7 17 − 6 16 transition. Thus, these transitions may help in detection of H 2 CSi in the interstellar medium.

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Rotational excitation of aluminium monofluoride (AlF) by He atom at low temperature

Cited by 19 publications

References 32 publications

Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

Astronomical detection of radioactive molecule 26AlF in the remnant of an ancient explosion

Molecular abundances in the inner layers of IRC +10216

Radiative transfer in silylidene molecule

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