Laboratory rotational spectroscopy of isotopic acetone, CH313C(O)CH3and13CH3C(O)CH3, and astronomical search in Sagittarius B2(N2)

Abstract

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 substituted13C isotopologs.Aims.We want to study the rotational spectra of CH313C(O)CH3and13CH3C(O)CH3and search for them in Sagittarius B2(N2).Methods.We investigated the laboratory rotational spectrum of isotopically enriched CH313C(O)CH3between 40 GHz and 910 GHz and of acetone between 36 GHz and 910 GHz in order to study13CH3C(O)CH3in 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)CH3and 63 new transitions of13CH3C(O)CH3in 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 statesv12 = 1 andv17 = 1 of CH3C(O)CH3improve only marginally. No transitrrrion of CH313C(O)CH3is clearly detected toward the hot molecular core Sgr B2(N2). However, we report a tentative detection of13CH3C(O)CH3with a12C/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)CH3and CH3C(O)CH3are reliable into the terahertz region. The spectrum of13CH3C(O)CH3should be revisited in the laboratory with an enriched sample. The torsionally excited statesv12 = 1 andv17 = 1 of CH3C(O)CH3were not reproduced satisfactorily in our models. Nevertheless, transitions pertaining to both states could be identified unambiguously in Sagittarius B2(N2).