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Detection of HF Toward PKS 1830-211, Search for Interstellar H2F+, and Laboratory Study of H2F+ and H2Cl+ Dissociative Recombination

K. Kawaguchi ; Sebastien Muller (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; John H. Black (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; T. Amano ; F. Matsushima ; R. Fujimori ; Y. Okabayahsi ; H. Nagahiro ; Y. Miyamoto ; J. Tang
Astrophysical Journal (0004-637X). Vol. 822 (2016), 2, p. Art. no. 115.
[Artikel, refereegranskad vetenskaplig]

We report extragalactic observations of two fluorine-bearing species, hydrogen fluoride (HF) and fluoronium (H2F+), in the z = 0.89 absorber in front of the lensed blazar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array. HF was detected toward both southwest and northeast images of the blazar, with column densities >3.4 × 1014 cm-2 and 0.18 × 1014 cm-2, respectively. H2F+ was not detected, down to an upper limit (3?) of 8.8 × 1011 cm-2 and an abundance ratio of [H2F+]/[HF] 1/386. We also searched for H2F+ toward the Galactic sources NGC 6334 I and W51C, and toward Galactic center clouds with the Herschel HIFI spectrometer.6 The upper limit on the column density was derived to be 2.5 × 1011 cm-2 in NGC 6334 I, which is 1/68 of that for H2Cl+. In constrast, the ortho transition of H2Cl+ is detected toward PKS 1830-211. To understand the small abundance of interstellar H2F+, we carried out laboratory experiments to determine the rate constants for the ion-electron recombination reaction by infrared time-resolved spectroscopy. The constants determined are ke(209 K) = (1.1 ± 0.3) ×10-7 cm3 s-1 and (0.46 ± 0.05) ×10-7 cm3 s-1 for H2F+ and H2Cl+, respectively. The difference in the dissociative recombination rates between H2F+ and H2Cl+ by a factor ?2 and the cosmic abundance ratio [F]/[Cl] ? 1/6 are not enough to explain the much smaller abundance of H2F+. The difference in the formation mechanism of H2F+ and H2Cl+ in interstellar space would be a major factor in the small abundance of H2F+.

Nyckelord: galaxies: individual (PKS 1830-211); ISM: individual objects (W31C, NGC 6334 I); ISM: molecules; methods: laboratory: molecular

Denna post skapades 2016-07-05. Senast ändrad 2017-01-30.
CPL Pubid: 238965


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