Millimetre wave spectrum of methyl mercaptan

We have detected interstellar acetic acid (CH 3 COOH) toward the hot core source W51e2. This is the first new source of interstellar CH 3 COOH since its discovery by Mehringer et al. toward the hot core source Sgr B2(N-LMH). In this paper, we report CH 3 COOH observations at two new frequencies toward Sgr B2(N-LMH) with the OVRO array and at 10 frequencies toward W51e2 with the Berkeley-Illinois-Maryland Association array. Toward Sgr B2(N-LMH) the agreement in positions, intensities, and velocities between the two lines from the previous study and the two new lines strongly indicates that all four CH 3 COOH lines are coming from a common source. Using all four detected transitions, we find an average column density of 6:1ð6Þ Â 10 15 cm À2 , a fractional abundance of ð0:8 6Þ Â 10 À10 relative to H 2 and ð3 6Þ Â 10 À2 relative to its isomer methyl formate (HCOOCH 3 ). Toward W51e2, we find a CH 3 COOH column density of 1:7ð5Þ Â 10 16 cm À2 with a fractional abundance of 1:7 Â 10 À9 relative to H 2 and ð1 6Þ Â 10 À2 relative to HCOOCH 3 . Furthermore, we find the distribution of CH 3 COOH toward W51e2 is coincident with HCOOCH 3 , thus suggesting a similar formation mechanism.

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“…(Lees & Mohammadi 1980). h The rest frequency coincides with the 5 0; 5 4 0; 4 transition of H 13 COOH at a frequency of 100,508.63 MHz.…”

Section: Column Densitiesmentioning

confidence: 75%

Acetic Acid in the Hot Cores of Sagitarrius B2(N) and W51

Remijan

Snyder

Liu

et al. 2002

ApJ

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“…Transition frequencies in the range of our survey were taken mainly from Lees & Mohammadi (1980) and Sastry et al (1986).…”

Section: Methyl Mercaptan Ch 3 Shmentioning

confidence: 99%

Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)

Беллоче

Müller

Menten

et al. 2013

A&A

389

523

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Context. The discovery of amino acids in meteorites fallen to Earth and the detection of glycine, the simplest of them, in samples returned from a comet to Earth strongly suggest that the chemistry of the interstellar medium is capable of producing such complex organic molecules and that they may be widespread in our Galaxy. Aims. Our goal is to investigate the degree of chemical complexity that can be reached in the interstellar medium, in particular in dense star-forming regions. Methods. We performed an unbiased, spectral line survey toward Sgr B2(N) and (M), two regions where high-mass stars are formed, with the IRAM 30 m telescope in the 3 mm atmospheric transmission window. Partial surveys at 2 and 1.3 mm were performed in parallel. The spectra were analyzed with a simple radiative transfer model that assumes local thermodynamic equilibrium but takes optical depth effects into account. Results. About 3675 and 945 spectral lines with a peak signal-to-noise ratio higher than 4 are detected at 3 mm toward Sgr B2(N) and (M), i.e. about 102 and 26 lines per GHz, respectively. This represents an increase by about a factor of two over previous surveys of Sgr B2. About 70% and 47% of the lines detected toward Sgr B2(N) and (M) are identified and assigned to 56 and 46 distinct molecules as well as to 66 and 54 less abundant isotopologues of these molecules, respectively. In addition, we report the detection of transitions from 59 and 24 catalog entries corresponding to vibrationally or torsionally excited states of some of these molecules, respectively, up to a vibration energy of 1400 cm −1 (2000 K). Excitation temperatures and column densities were derived for each species but should be used with caution. The rotation temperatures of the detected complex molecules typically range from ∼50 to 200 K. Among the detected molecules, aminoacetonitrile, n-propyl cyanide, and ethyl formate were reported for the first time in space based on this survey, as were five rare isotopologues of vinyl cyanide, cyanoacetylene, and hydrogen cyanide. We also report the detection of transitions from within twelve new vibrationally or torsionally excited states of known molecules. Absorption features produced by diffuse clouds along the line of sight are detected in transitions with low rotation quantum numbers of many simple molecules and are modeled with ∼30-40 velocity components with typical linewidths of ∼3-5 km s −1 . Conclusions. Although the large number of unidentified lines may still allow future identification of new molecules, we expect most of these lines to belong to vibrationally or torsionally excited states or to rare isotopologues of known molecules for which spectroscopic predictions are currently missing. Significant progress in extending the inventory of complex organic molecules in Sgr B2(N) and deriving tighter constraints on their location, origin, and abundance is expected in the near future thanks to an ongoing spectral line survey at 3 mm with ALMA in its cycles 0 and 1. The present single-dish surve...

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“…The entry is based on Xu et al (2012). Extensive terahertz and far-IR data were combined with previous data, which include data in the range of our survey from Lees & Mohammadi (1980) with additional data mainly from Sastry et al (1986) and Bettens et al (1999). Dipole moment components of |µ a | = 1.312 D and |µ b | = 0.758 D were cited by Tsunekawa et al (1989).…”

Section: Methanethiol Ch 3 Shmentioning

confidence: 99%

Exploring molecular complexity with ALMA (EMoCA): Alkanethiols and alkanols in Sagittarius B2(N2)

Müller

Беллоче

et al. 2016

A&A

139

157

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Context. Over the past five decades, radio astronomy has shown that molecular complexity is a natural outcome of interstellar chemistry, in particular in star forming regions. However, the pathways that lead to the formation of complex molecules are not completely understood and the depth of chemical complexity has not been entirely revealed. In addition, the sulfur chemistry in the dense interstellar medium is not well understood. Aims. We want to know the relative abundances of alkanethiols and alkanols in the Galactic center source Sagittarius B2(N2), the northern hot molecular core in Sgr B2(N), whose relatively small line widths are favorable for studying the molecular complexity in space. Methods. We investigated spectroscopic parameter sets that were able to reproduce published laboratory rotational spectra of ethanethiol and studied effects that modify intensities in the predicted rotational spectrum of ethanol. We used the Atacama Large Millimeter Array (ALMA) in its Cycles 0 and 1 for a spectral line survey of Sagittarius B2(N) between 84 and 114.4 GHz. These data were analyzed by assuming local thermodynamic equilibrium (LTE) for each molecule. Our observations are supplemented by astrochemical modeling; a new network is used that includes reaction pathways for alkanethiols for the first time. Results. We detected methanol and ethanol in their parent 12 C species and their isotopologs with one 12 C atom substituted by 13 C; the latter were detected for the first time unambiguously in the case of ethanol. The 12 C/ 13 C ratio is ∼25 for both molecules. In addition, we identified CH OH ratio of ∼7.3. Upper limits were derived for the next larger alkanols normal-and iso-propanol. We observed methanethiol, CH 3 SH, also known as methyl mercaptan, including torsionally excited transitions for the first time. We also identified transitions of ethanethiol (or ethyl mercaptan), though not enough to claim a secure detection in this source. The ratios CH 3 SH to C 2 H 5 SH and C 2 H 5 OH to C 2 H 5 SH are 21 and 125, respectively. In the process of our study, we noted severe discrepancies in the intensities of observed and predicted ethanol transitions and propose a change in the relative signs of the dipole moment components. In addition, we determined alternative sets of spectroscopic parameters for ethanethiol. The astrochemical models indicate that substantial quantities of both CH 3 SH and C 2 H 5 SH may be produced on the surfaces of dust grains, to be later released into the gas phase. The modeled ratio CH 3 SH/C 2 H 5 SH = 3.1 is lower than the observed value of 21; the model value appears to be affected most by the underprediction of CH 3 SH relative to CH 3 OH and C 2 H 5 OH, as judged by a very high CH 3 OH/CH 3 SH ratio. Conclusions. The column density ratios involving methanol, ethanol, and methanethiol in Sgr B2(N2) are similar to values reported for Orion KL, but those involving ethanethiol are significantly different and suggest that the detection of ethanethiol reported toward Orion KL ...

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Millimetre wave spectrum of methyl mercaptan

Cited by 30 publications

References 8 publications

Acetic Acid in the Hot Cores of Sagitarrius B2(N) and W51

Acetic Acid in the Hot Cores of Sagitarrius B2(N) and W51

Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)

Exploring molecular complexity with ALMA (EMoCA): Alkanethiols and alkanols in Sagittarius B2(N2)

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