Laboratory and astronomical identification of cyclopropenylidene, C3H2

Thaddeus, P.; Vrtilek, J. M.; Gottlieb, C. A.

doi:10.1086/184581

Cited by 351 publications

(204 citation statements)

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“…The ring molecule cyclo-propenylidene c-C 3 H 2 is a fairly ubiquituous interstellar species (e.g., Thaddeus et al 1985b;Cox et al 1988;Madden et al 1989). We detect 2 ortho and 2 para lines, yielding an ortho/para ratio of 2.8 ± 0.1, comparable to the statistical weight 3:1.…”

Section: B10 C-c 3 Hsupporting

confidence: 49%

Molecules atz= 0.89

Müller

Beelen

Guèlin

et al. 2011

A&A

163

284

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We present the results of a 7 mm spectral survey of molecular absorption lines originating in the disk of a z = 0.89 spiral galaxy located in front of the quasar PKS 1830−211. Our survey was performed with the Australia Telescope Compact Array and covers the frequency interval 30-50 GHz, corresponding to the rest-frame frequency interval 57-94 GHz. A total of 28 different species, plus 8 isotopic variants, were detected toward the south-west absorption region, located about 2 kpc from the center of the z = 0.89 galaxy, which therefore has the largest number of detected molecular species of any extragalactic object so far. The results of our rotation diagram analysis show that the rotation temperatures are close to the cosmic microwave background temperature of 5.14 K that we expect to measure at z = 0.89, whereas the kinetic temperature is one order of magnitude higher, indicating that the gas is subthermally excited. The molecular fractional abundances are found to be in-between those in typical Galactic diffuse and translucent clouds, and clearly deviate from those observed in the dark cloud TMC 1 or in the Galactic center giant molecular cloud Sgr B2. The isotopic ratios of carbon, nitrogen, oxygen, and silicon deviate significantly from the solar values, which can be linked to the young age of the z = 0.89 galaxy and a release of nucleosynthesis products dominated by massive stars. Toward the north-east absorption region, where the extinction and column density of gas is roughly one order of magnitude lower than toward the SW absorption region, only a handful of molecules are detected. Their relative abundances are comparable to those in Galactic diffuse clouds. We also report the discovery of several new absorption components, with velocities spanning between −300 and +170 km s −1 . Finally, the line centroids of several species (e.g., CH 3 OH, NH 3 ) are found to be significantly offset from the average velocity. If caused by a variation in the proton-to-electron mass ratio μ with redshift, these offsets yield an upper limit | Δμ μ | < 4×10 −6 , which takes into account the kinematical noise produced by the velocity dispersion measured from a large number of molecular species.

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Section: B10 C-c 3 Hsupporting

confidence: 49%

Molecules atz= 0.89

Müller

Beelen

Guèlin

et al. 2011

A&A

163

284

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“…Three are linear or near linear, and one is cyclic. The cyclic isomer is the most stable and is very abundant in interstellar molecular clouds, but linear HCCCH may occur there also (Thaddeus et al 1985). Helbert et al (2005) do not explicitly state which C 3 H 2 isomer is considered in their reaction scheme.…”

Section: Discussionmentioning

confidence: 99%

On the Origin of Cometary C₂and C₃: Hydrogen Atom Migration in Diacetylene?

Heymann

2008

ApJ

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The photolysis of C 10 H 2 in air-saturated hexane by 253.6 nm photons yields the polyyne C 8 H 2 in approximately 5% of all C 10 H 2 disappearances; perhaps due to the migration of the hydrogen atom on À1 (I use the symbol Àn to designate the specific carbon atom number n in the chain; À1 is carbon atom 1) to À3 in the electronically excited C 10 H Ã 2 molecule followed by the rupture of the À2-À3 carbon-carbon bond. C 6 H 2 and C 12 H 2 were not seen to form. This new result strengthens the hypothesis that hydrogen migration along carbon chains of photon-excited polyynes followed by the rupture of one carbon bond could be very common among these compounds. It is suggested here that diacetylene forms photochemically from acetylene in the cometary coma followed by the swift photochemical formation of C 2 from diacetylene by hydrogen migration from À1 to À3 followed by the rupture of the À2-À3 carboncarbon bond. Hydrogen migration from À1 to À4 in excited diacetylene followed by the rupture of the À3-À4 carbon bond might form cometary C 3 . Neither C 2 nor C 3 were detected in the current study. Their formation by hydrogen migration is therefore hypothetical but the case for C 2 is observationally stronger than for C 3 . Removal of air from the solution increased the disappearance rate of C 10 H 2 by a factor of almost 10 3 , which implies that the excited molecule is in a triplet state with an estimated lifetime of 160 s.

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“…http://spec.jpl.nasa.gov), the electric dipole moment, asymmetric rotor line strengths and excitation above the ground state (e.g. Thaddeus et al 1985;Vrtilek et al 1987;Lovas & Suenram 1989) known, a column density assuming LTE and optically thin emission can be derived.…”

Section: Hmentioning

confidence: 99%

Dense gas in nearby galaxies

Wang

Henkel²,

Chin

et al. 2004

A&A

129

184

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Abstract.A multi-line millimeter-wave study of the nearby starburst galaxy NGC 4945 has been carried out using the Swedish-ESO Submillimeter Telescope (SEST). The study covers the frequency range from 82 GHz to 354 GHz and includes 80 transitions of 19 molecules. 1.3 mm continuum data of the nuclear source are also presented. An analysis of CO and 1.3 mm continuum fluxes indicates that the conversion factor between H 2 column density and CO J = 1−0 integrated intensity is smaller than in the galactic disk by factors of 5−10. A large number of molecular species indicate the presence of a prominent high density interstellar gas component characterized by n H 2 ∼ 10 5 cm −3 . Some spectra show Gaussian profiles. Others exhibit two main velocity components, one at ∼450 km s −1 , the other at ∼710 km s −1 . While the gas in the former component has a higher linewidth, the latter component arises from gas that is more highly excited as is indicated by HCN, HCO + and CN spectra. Abundances of molecular species are calculated and compared with abundances observed toward the starburst galaxies NGC 253 and M 82 and galactic sources. Apparent is an "overabundance" of HNC in the nuclear environment of NGC 4945. While the HNC/HCN J = 1−0 line intensity ratio is ∼0.5, the HNC/HCN abundance ratio is ∼1. From a comparison of K a = 0 and 1 HNCO line intensities, an upper limit to the background radiation of 30 K is derived. While HCN is subthermally excited (T ex ∼ 8 K), CN is even less excited (T ex ∼ 3−4 K), indicating that it arises from a less dense gas component and that its N = 2−1 line can be optically thin even though its N = 1−0 emission is moderately optically thick. Overall, fractional abundances of NGC 4945 suggest that the starburst has reached a stage of evolution that is intermediate between those observed in NGC 253 and M 82. Carbon, nitrogen, oxygen and sulfur isotope ratios are also determined. Within the limits of uncertainty, carbon and oxygen isotope ratios appear to be the same in the nuclear regions of NGC 4945 and NGC 253. S ratios (6.4 ± 0.3, 195 ± 45, 105 ± 25 and 13.5 ± 2.5 in NGC 4945, respectively) appear to be characteristic properties of a starburst environment in which massive stars have had sufficient time to affect the isotopic composition of the surrounding interstellar medium.

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Laboratory and astronomical identification of cyclopropenylidene, C3H2

Cited by 351 publications

References 0 publications

Molecules atz= 0.89

Molecules atz= 0.89

On the Origin of Cometary C₂and C₃: Hydrogen Atom Migration in Diacetylene?

Dense gas in nearby galaxies

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Laboratory and astronomical identification of cyclopropenylidene, C3H2

Cited by 351 publications

References 0 publications

Molecules atz= 0.89

Molecules atz= 0.89

On the Origin of Cometary C2and C3: Hydrogen Atom Migration in Diacetylene?

Dense gas in nearby galaxies

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On the Origin of Cometary C₂and C₃: Hydrogen Atom Migration in Diacetylene?