Radio Detection of Interstellar CH

Rydbeck, O. E. H.; Elldér, J.; Irvine, William M.

doi:10.1038/246466a0

Cited by 107 publications

(53 citation statements)

References 4 publications

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“…The lowest pure rotational transition lies outside of the spectral range available to radio astronomers, but lambda doubling transitions can be used to detect SiH. Similar radiofrequency transitions have been successfully used for the detection of OH and CH in the interstellar medium (26,27). Wilson and Richards (28) obtained a ⌳-doubling frequency of 2940 Ϯ 300 MHz for J ϭ 0.5 by extrapolating the ⌳-doubling from high rotational levels populated in the optical experiment of Douglas and Elliott (5).…”

Section: Introductionmentioning

confidence: 96%

Fourier Transform Emission Spectroscopy of theA2Δ–X2Π Transition of SiH and SiD

Ram

Engleman

Bernath

1998

Journal of Molecular Spectroscopy

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Section: Introductionmentioning

confidence: 96%

Fourier Transform Emission Spectroscopy of theA2Δ–X2Π Transition of SiH and SiD

Ram

Engleman

Bernath

1998

Journal of Molecular Spectroscopy

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“…It was one of the first interstellar molecules identified (1,2), by means of detection in the optical band of a single line [R 2 (1)] near 4,300 Å of the A 2 ⌬ 3 X 2 ͟ electronic transition. It has now been observed in other parts of the spectrum as follows: (i) in the radio, by detection of lambda-doubling transitions near 3.3 GHz (3)(4)(5) in the lowest rotational level (J ϭ 1͞2) of the X 2 ͟ 1/2 state; (ii) near 700 MHz (6) in the lowest rotational level of the upper fine structure ladder (X 2 ͟ 3/2 ); (iii) in the far-infrared (FIR), by detection in both absorption (7) and emission (8) of its fundamental rotational transitions at 149.09 and 149.39 m; and (iv) in the far UV, including the diffuse feature at 1369.13 Å (9). There is little astronomical data on the rare isotopic species 13 CH, but some of its lines have been identified in the solar spectrum (10).…”

mentioning

confidence: 99%

Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals

McCarthy

Mohamed

Brown

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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By Fourier transform microwave spectroscopy, lambda-doubling transitions of 12 CH and 13 CH in the lowest rotational levels of the X 2 ͟1/2 ground state have been directly detected, which has not been done previously. For both radicals, hyperfine-split lines have been measured to an accuracy of better than 1 ppm between 3 and 15 GHz, an improvement of at least 2 orders of magnitude over previous laboratory data. The measured frequencies have been combined with all previous data for CH and 13 CH in the v ‫؍‬ 0 level of the X 2 ͟ electronic state to determine improved hyperfine parameters. The production of CH from various gases also has been studied and, with methanol, the yield of CH relative to OH. Astronomical studies of CH in higher rotational levels and 13 CH can now be undertaken on the basis of the present work.microwave spectroscopy ͉ molecular data ͉ radio astronomy T he CH radical is widely distributed in astronomical sources, observed in planetary atmospheres, comets, HI and HII regions, dark molecular clouds, and planetary nebulae. It was one of the first interstellar molecules identified (1, 2), by means of detection in the optical band of a single line [R 2 (1)] near 4,300 Å of the A 2 ⌬ 3 X 2 ͟ electronic transition. It has now been observed in other parts of the spectrum as follows: (i) in the radio, by detection of lambda-doubling transitions near 3.3 GHz (3-5) in the lowest rotational level (J ϭ 1͞2) of the X 2 ͟ 1/2 state; (ii) near 700 MHz (6) in the lowest rotational level of the upper fine structure ladder (X 2 ͟ 3/2 ); (iii) in the far-infrared (FIR), by detection in both absorption (7) and emission (8) of its fundamental rotational transitions at 149.09 and 149.39 m; and (iv) in the far UV, including the diffuse feature at 1369.13 Å (9). There is little astronomical data on the rare isotopic species 13 CH, but some of its lines have been identified in the solar spectrum (10).Because of the astronomical importance of CH, considerable effort has been devoted in the laboratory to measure its rotational spectrum. Early studies by laser magnetic resonance (ref.11 and references therein) allowed some of the more interesting lines to be predicted to an uncertainty of Ϸ2 MHz. Since then, more accurate FIR spectra (good to 100 kHz; ref. 12) and submillimeter-wave spectra (good to 30-100 kHz; ref. 13) have been obtained, as well as microwave-optical double resonance (MODR) measurements (14, 15) and a few centimeter-wave measurements at fairly high J ϳ 6.5 (16) to better pin down the lambda-doubling intervals. 13 CH has been studied by some of the same techniques (17-19), but owing to the lack of tunable FIR measurements, its rotational spectrum until now could only be predicted to a few megahertz.Although much laboratory spectroscopy has already been done on CH and 13 CH, still more is needed: many of the lambda-doubling transitions have not been measured to high precision, and only a small number of the FIR spin-rotational intervals have been detected at adequately high signal-to-noise. It is parti...

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“…CH was one of the first molecules to be identified in the interstellar medium (ISM) through the detection of a single line in the A 2 D-X 2 P electronic transition [31,32]. Its presence in the ISM was dramatically confirmed in 1973 by radio astronomy through the detection of lambda-doubling transitions in the lowest rotational level (J ¼ 1=2) around 3.3 GHz [2]. More recently, 12 CH has also been detected in the ISM by the observation of the J ¼ 3=2 À 1=2, F 2 À F 2 transition at 149 lm using instruments on the Kuiper Airborne Observatory [33] and on the ISO satellite [34].…”

Section: Discussionmentioning

confidence: 98%

“…Consequently, there is a strong incentive to characterise the molecule in as many of its isotopic modifications as possible. Although the principal properties of the dominant isotopomer 12 CH have been known for a long time [1], the most detailed information on the molecule in its ground state has been gathered quite recently [2][3][4][5][6]. The deuterated form, CD, is also well characterised from studies of its optical [7], infrared [8,9] and far-infrared spectra [10].…”

Section: Introductionmentioning

confidence: 99%