Laboratory and Astronomical Detection of the SiP Radical (X2Π i ): More Circumstellar Phosphorus
Abstract
The millimeter-wave spectrum of the SiP radical (X2Πi) has been measured in the laboratory for the first time using direct-absorption methods. SiP was created by the reaction of phosphorus vapor and SiH4 in argon in an AC discharge. Fifteen rotational transitions (J + 1 ← J) were measured for SiP in the Ω = 3/2 ladder in the frequency range 151-533 GHz, and rotational, lambda doubling, and phosphorus hyperfine constants determined. Based on the laboratory measurements, SiP was detected in the circumstellar shell of IRC+10216, using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1 mm and 2 mm, respectively. Eight transitions of SiP were searched: four were completely obscured by stronger features, two were uncontaminated (J = 13.5 → 12.5 and 16.5 → 15.5), and two were partially blended with other lines (J = 8.5 → 7.5 and 17.5 → 16.5). The SiP line profiles were broader than expected for IRC+10216, consistent with the hyperfine splitting. From non-LTE radiative transfer modeling, SiP was found to have a shell distribution with a radius ~300 R *, and an abundance, relative to H2, of f ~ 2 × 10-9. From additional modeling, abundances of 7 × 10-9 and 9 × 10-10 were determined for CP and PN, respectively, both located in shells at 550-650 R *. SiP may be formed from grain destruction, which liberates both phosphorus and silicon into the gas phase, and then is channeled into other P-bearing molecules such as PN and CP.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2022
- DOI:
- 10.3847/2041-8213/ac9d9b
- Bibcode:
- 2022ApJ...940L..11K
- Keywords:
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- Astrochemistry;
- Circumstellar envelopes;
- Molecular spectroscopy;
- Evolved stars;
- Chemical abundances;
- Interstellar molecules;
- Asymptotic giant branch stars;
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