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 ...

The ground state rotational spectra of 2-fluoropyridine and 3-fluoropyridine have been investigated using both Fourier transform microwave (FTMW) and chirped pulse Fourier transform microwave (cp-FTMW) spectroscopies. In addition to the parent species, the spectra of the 13C and 15N singly substituted isotopologues were recorded in the 8–23 GHz region in natural abundance. The rotational constants determined for the seven isotopologues of each were used to calculate relevant geometric parameters including the bond distances and angles of the pyridine ring backbone. The derived structures show a more pronounced deviation from the pyridine ring geometry when the fluorine substituent is ortho to nitrogen which is consistent with ab initio predictions at various levels of theory. Analysis of the 14N hyperfine structure provided an additional source of information about the electronic structure surrounding the nitrogen atom as a function of fluorine substitution. Together, the experimental results are consistent with a bonding model that involves hyperconjugation whereby fluorine donates electron density from its lone pair into the π-system of pyridine.

The rotational spectrum of a "new" isomer of OCS-CO(2) has been measured between 5 and 18 GHz using Fourier transform microwave spectroscopy. Both a- and b-type transitions of the parent dimer and the (13)CO(2)-containing isotopologue were fit and the resulting spectroscopic constants confirm that this is the planar O-interior, not-quite-as-parallel isomer that was experimentally observed for the first time in the recent infrared investigation of Dehghany et al. [J. Chem. Phys. 130, 224310 (2009)]. As in the infrared study, the microwave transitions of this isomer appear stronger than those of the previously reported lower energy isomer of OCS-CO(2) when helium is used as the backing gas for the supersonic expansion.

Microwave spectra and structure of an isoxazole-CO Van der Waals complex

Rotational spectra of the Ar–ND3 van der Waals complex were measured in the frequency range between 4 and 19 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The isotopomers studied include those with ND3, NHD2, and NH2D. A tunneling splitting due to the inversion of the ammonia subunit within the ground state of the complex was observed for all three isotopomers. This splitting cannot be measured in Ar–NH3 for spin statistical reasons. Nuclear quadrupole hyperfine structure of rotational transitions arising from the N14 nucleus was resolved and the corresponding nuclear quadrupole coupling constants were determined. A smaller nuclear quadrupole splitting arising from the deuterium nuclei was observed but not resolved. The ground state spectroscopic constants are compared with experimental and theoretical data previously reported for Ar–NH3. Additional transitions were observed for Ar–ND3 and assigned to the two inversion tunnelling states of an excited internal rotor state. A fit of the spectroscopic constants for these two states suggests the presence of a Coriolis perturbation along the lines of that observed in the microwave spectrum of Ar–NH3.