Millimeter-Wave and Vibrational State Assignments for the Rotational Spectrum of Glycolaldehyde

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Glycolaldehyde (CHOCH2OH), the simplest two-carbon α-hydroxy aldehyde, has become of great interest in the field of astrochemistry due to its recent detection toward the Sagittarius B2 (N-LMH) molecular cloud. The original interstellar identification was based on an extrapolation of prior microwave rotational spectroscopy of glycolaldehyde. The millimeter and submillimeter spectra of this molecule from 128 to 354 GHz were subsequently measured after the interstellar detection. We present here the millimeter spectrum of this molecule from 72 to 122.5 GHz along with a combined millimeter and submillimeter pure rotational analysis of the ground and the first three vibrationally excited states of glycolaldehyde that enables a more complete molecular partition function to be determined.These results show that excited vibrational state contributions to the partition function are an important consideration when determining the column density of a molecule with low-lying torsional states.