HYDROXYACETONE (CH3COCH2OH): A COMBINED MICROWAVE AND MILLIMETER-WAVE LABORATORY STUDY AND ASSOCIATED ASTRONOMICAL SEARCH

A combined laboratory and astronomical investigation has been conducted on the methyl sugar hydroxyacetone (CH3COCH2OH). Rotational transitions of this species in the ground torsional state (vt = 0) were recorded using both millimeter-wave direct absorption techniques and Fourier transformmicrowave spectroscopy. A total of 1145 lines of CH3COCH2OH were analyzed in the frequency range 4 to 180 GHz, including transitions arising from both A- and E-symmetry species. A modified rho-axis method Hamiltonian was needed for the analysis because of the presence of perturbations resulting from the torsional motion of the methyl group in thismolecule. Assignment of theE-species was particularly problematic as a consequence of significant mixing between the ground and torsionally excited levels. The complete data set was fitted using 21 spectroscopic parameters and had a global rms of 90 kHz; the barrier to internal rotation was established to be 65.3560(22) cm1. An astronomical search was subsequently conducted for hydroxy-acetone at 2 and 3 mm using the 12 m telescope of the Arizona Radio Observatory. Twenty-eight favorable transitions arising from both A- and E-species, each consisting of collapsed quartets, were searched for toward Sgr B2(N). Al-though credible featureswere detected at several frequencies of hydroxyacetone, therewere a sufficient number of miss-ing lines to rule out an interstellar detection. An upper limit to the column density of Ntot < 5; 1012 cm2 was derived for CH3COCH2OH in Sgr B2(N), indicating that this species is an order of magnitude less abundant than glycolaldehyde (CH2OHCHO). Subject headinggs: astrobiology — astrochemistry — ISM: abundances — ISM: individual (Sagittarius B2)