Laboratory rotational spectroscopy of isotopic acetone, CH313C(O)CH3 and 13CH3C(O)CH3, and astronomical search in Sagittarius B2(N2)
Abstract
We want to study the rotational spectra of CH313C(O)CH3 and 13CH3C(O)CH3 and search for them in Sagittarius B2(N2). 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 ALMA. Discrepancies between predictions of the main isotopic species and the ALMA spectrum prompted us to revisit the rotational spectrum of this isotopolog. 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 lines 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 v 12 = 1 and v 17 = 1 of CH3C(O)CH3 improve only marginally. No transition 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. 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. Transitions pertaining to the torsionally excited states v 12 = 1 and v 17 = 1 of CH3C(O)CH3 could be identified unambiguously in Sagittarius B2(N2).