SIMBAD references

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. 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. 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 114.4GHz. 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. We detected methanol and ethanol in their parent ¹²C species and their isotopologs with one ¹²C atom substituted by ¹³C; the latter were detected for the first time unambiguously in the case of ethanol. The ¹²C/¹³C ratio is ∼25 for both molecules. In addition, we identified CH₃¹⁸OH with a ¹⁶O/¹⁸O ratio of ∼180 and a ¹³CH₃OH/CH₃¹⁸OH ratio of ∼7.3. Upper limits were derived for the next larger alkanols normal- and iso-propanol. We observed methanethiol, CH₃SH, 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 CH₃SH to C₂H₅SH and C₂H₅OH to C₂H₅SH 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 CH₃SH and C₂H₅SH may be produced on the surfaces of dust grains, to be later released into the gas phase. The modeled ratio CH₃SH/C₂H₅SH=3.1 is lower than the observed value of >21; the model value appears to be affected most by the underprediction of CH₃SH relative to CH₃OH and C₂H₅OH, as judged by a very high CH₃OH/CH₃SH ratio. 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 is uncertain. Our chemical model presently does not permit the prediction of sufficiently accurate column densities of alkanethiols or their ratios among alkanethiols and alkanols. Therefore, additional observational results are required to establish the level of C₂H₅SH in the dense and warm interstellar medium with certainty.