Rotational and rovibrational spectra of methyl cyanide were recorded to analyze interactions in low-lying vibrational states and to construct line lists for radio astronomical observations in space as well as for infrared spectroscopic investigations of planetary atmospheres. The rotational spectra cover large portions of the 36−1627 GHz region. In the infrared (IR), a spectrum was recorded for this study in the region of 2ν 8 around 717 cm −1 with assignments covering 684−765 cm −1. Additional spectra in the ν 8 region were used to validate the analysis. Information on the K level structure of CH 3 CN is almost exclusively obtained from IR spectra, as are basics of the J level structure. The large amount and the high accuracy of the rotational data improves knowledge of the J level structure considerably. Moreover, since these data extend to much higher J and K quantum numbers, they allowed us to investigate for the first time in depth local interactions between these states which occur at high K values. In particular, we have detected several interactions between 8 = 1 and 2. Notably, there is a strong ∆ 8 = ±1, ∆K = 0, ∆l = ±3 Fermi resonance between 8 = 1 −1 and 8 = 2 +2 at K = 14. Pronounced effects in the spectrum are also caused by resonant ∆ 8 = ±1, ∆K = ∓2, ∆l = ±1 interactions between 8 = 1 and 2 at K = 13, l = −1/K = 11, l = 0 and at K = 15, l = +1/K = 13, l = +2. An equivalent resonant interaction occurs between K = 14 of the ground vibrational state and K = 12, l = +1 of 8 = 1 for which we present the first detailed account. A preliminary account was given in an earlier study on the ground vibrational state. Similar resonances were found for CH 3 CCH and, more recently, for CH 3 NC, warranting comparison of the results. From data pertaining to 8 = 2, we also investigated rotational interactions with 4 = 1 as well as ∆ 8 = ±1, ∆K = 0, ∆l = ±3 Fermi interactions between 8 = 2 and 3. We have derived N 2-and self-broadening coefficients for the ν 8 , 2ν 8 − ν 8 , and 2ν 8 bands from previously determined ν 4 values. Subsequently, we determined transition moments and intensities for the three IR bands.

Context. The saturated n-propyl cyanide was recently detected in Sagittarius B2(N). The next largest unbranched alkyl cyanide is n-butyl cyanide. Aims. We provide accurate rest frequency predictions beyond the millimeter wave range to search for this molecule in the Galactic center source Sagittarius B2(N) and facilitate its detection in space. Methods. We investigated the laboratory rotational spectrum of n-butyl cyanide between 75 GHz and 348 GHz. We searched for emission lines produced by the molecule in our sensitive IRAM 30 m molecular line survey of Sagittarius B2(N). Results. We identified more than one thousand rotational transitions in the laboratory for each of the three conformers for which limited data had been obtained previously in a molecular beam microwave study. The quantum number range was greatly extended to J ≈ 120 or more and K a > 35, resulting in accurate spectroscopic parameters and accurate rest frequency calculations up to about 500 GHz for strong to moderately weak transitions of the two lower energy conformers. Upper limits to the column densities of N ≤ 3 × 10 15 cm −2 and 8 × 10 15 cm −2 were derived towards Sagittarius B2(N) for the two lower energy conformers, anti-anti and gauche-anti, respectively. Conclusions. Our present data will be helpful for identifying n-butyl cyanide at millimeter or longer wavelengths with radio telescope arrays such as ALMA, NOEMA, or EVLA. In particular, its detection in Sagittarius B2(N) with ALMA seems feasible.

Context. Ethanediol is one of the largest complex organic molecules detected in space thus far. It has been found in different types of molecular clouds. The two propanediol isomers are the next larger diols. Hence, they are viable candidates to be searched for in space. Aims. We wish to provide sufficiently large and accurate sets of spectroscopic parameters of 1, 2-propanediol to facilitate searches for this molecule at millimeter and longer submillimeter wavelengths. Methods. We recorded rotational spectra of 1, 2-propanediol in three wide frequency windows between 38 and 400 GHz. Results. We made extensive assignments for the three lowest energy conformers to yield spectroscopic parameters up to eighth order of angular momentum. Conclusions. Our present data will be helpful for identifying 1, 2-propanediol at moderate submillimeter or longer wavelengths with radio telescope arrays such as ALMA, NOEMA, or EVLA. In particular, its detection with ALMA in sources, in which ethanediol was detected, appears to be promising.

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Context. Spectral lines of minor isotopic species of molecules that are abundant in space may also be detectable. Their respective isotopic ratios may provide clues about the formation of these molecules. Emission lines of acetone in the hot molecular core Sagittarius B2(N2) are strong enough to warrant a search for its singly substituted 13C isotopologs. Aims. We want to study the rotational spectra of CH313C(O)CH3 and 13CH3C(O)CH3 and search for them in Sagittarius B2(N2). Methods. We investigated the laboratory rotational spectrum of isotopically enriched CH313C(O)CH3 between 40 GHz and 910 GHz and of acetone between 36 GHz and 910 GHz in order to study 13CH3C(O)CH3 in natural isotopic composition. In addition, we searched for emission lines produced by these species in a molecular line survey of Sagittarius B2(N) carried out with the Atacama Large Millimeter/submillimeter Array (ALMA). Discrepancies between predictions of the main isotopic species and the ALMA spectrum prompted us to revisit the rotational spectrum of this isotopolog. Results. We assigned 9711 new transitions of CH313C(O)CH3 and 63 new transitions of 13CH3C(O)CH3 in the laboratory spectra. More than 1000 additional transitions were assigned for the main isotopic species. We modeled the ground state data of all three isotopologs satisfactorily with the ERHAM program. We find that models of the torsionally excited states v12 = 1 and v17 = 1 of CH3C(O)CH3 improve only marginally. No transitrrrion of CH313C(O)CH3 is clearly detected toward the hot molecular core Sgr B2(N2). However, we report a tentative detection of 13CH3C(O)CH3 with a 12C/13C isotopic ratio of 27 that is consistent with the ratio previously measured for alcohols in this source. Several dozens of transitions of both torsional states of the main isotopolog are detected as well. Conclusion. Our predictions of CH313C(O)CH3 and CH3C(O)CH3 are reliable into the terahertz region. The spectrum of 13CH3C(O)CH3 should be revisited in the laboratory with an enriched sample. The torsionally excited states v12 = 1 and v17 = 1 of CH3C(O)CH3 were not reproduced satisfactorily in our models. Nevertheless, transitions pertaining to both states could be identified unambiguously in Sagittarius B2(N2).