Calcium Chemistry in Carbon-rich Circumstellar Environments: The Laboratory and Astronomical Discovery of Calcium Dicarbide, CaC2

被引：1

作者：

Gupta, H. ^{[1
,2
]}

Changala, P. B. ^{[1
]}

Cernicharo, J. ^{[3
]}

Pardo, J. R. ^{[3
]}

Agundez, M. ^{[3
]}

Cabezas, C. ^{[3
]}

Tercero, B. ^{[4
]}

Guelin, M. ^{[5
]}

McCarthy, M. C. ^{[1
]}

机构：

[1] Ctr Astrophys Harvard & Smithsonian, Cambridge, MA 02138 USA

[2] Natl Sci Fdn, Alexandria, VA 22314 USA

[3] Inst Fis Fundamental, Dept Mol Astrophys, CSIC, Serrano 121, Madrid 28006, Spain

[4] Observ Astron Nacl, IGN, C Alfonso 123, Madrid 28014, Spain

[5] Inst Radioastron Millimetr, 300 Rue Piscine, F-38406 St Martin Dheres, France

来源：

ASTROPHYSICAL JOURNAL LETTERS | 2024年 / 966卷 / 02期

基金：

美国国家科学基金会; 欧洲研究理事会;

关键词：

AB-INITIO; IRC+10216; ENVELOPE; INTERSTELLAR; SPECTROSCOPY; TRANSITION; MOLECULE; STATES; MGCN+; C-2;

D O I：

10.3847/2041-8213/ad3336

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

Calcium dicarbide, CaC2, has been characterized at high resolution in the laboratory, and its main isotopologue, (CaC2)-Ca-40, has been assigned to 14 rotational emission lines between 14 and 115 GHz, including 12 previously unassigned lines, in the expanding molecular envelope of the evolved carbon star IRC+10216. Aided by high-level quantum calculations and measurements of multiple isotopologues, CaC2 is determined to be a T-shaped molecule with a highly ionic bond linking the metal atom to the C-2 unit, very similar in structure to isovalent magnesium dicarbide (MgC2). The excitation of CaC2 is characterized by a very low rotational temperature of 5.8 +/- 0.6 K and a kinetic temperature of 36 +/- 16 K, similar to values derived for MgC2. On the assumption that the emission originates from a 30 '' shell in IRC+10216, the column density of CaC2 is (5.6 +/- 1.7) x 10(11) cm(-2). CaC2 is only the second Ca-bearing molecule besides CaNC and only the second metal dicarbide besides MgC2 identified in space. Owing to the similarity between the predicted ion-molecule chemistry of Ca and Mg, a comparison of the CaC2 abundance with that of MgC2 and related species permits empirical inferences about the radiative association-dissociative recombination processes postulated to yield metal-bearing molecules in IRC+10216 and similar objects.

引用

页数：9

共 6 条

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INDIAN JOURNAL OF PHYSICS, 2020, 94 (12) : 1869 - 1874
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1600, EDP Sciences (568):
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[6] Investigation of silicon dicarbide (SiC2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {SiC}_2$$\end{document}) in circumstellar envelopes around carbon-rich AGB stars
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