Laboratory rotational spectrum and astronomical search for methoxyacetaldehyde.

Context: Methoxyacetaldehyde belongs to a group of structural isomers with the general formula C3 H6 O2 , of which methyl acetate and ethyl formate are known interstellar molecules. Rotational data available for methoxyacetaldehyde are limited to 40 GHz, which makes predictions at higher frequencies rather uncertain.

Aims: The aim of this work is to provide accurate experimental frequencies of methoxyacetaldehyde in the millimeter-wave region to support its detection in the interstellar medium.

Methods: The rotational spectrum of methoxyacetaldehyde was recorded at room-temperature from 75 to 120 GHz and from 170 to 310 GHz using the millimeter-wave spectrometer in Valladolid. Additional measurements were also performed at conditions of supersonic expansion from 6 to 18 GHz. The assigned rotational transitions were analyzed using the S -reduced semirigid-rotor Hamiltonian.

Results: We newly assigned over 1000 lines for the most stable conformer of methoxyacetaldehyde in its ground state and five lowest excited vibrational states, and precise sets of spectroscopic constants were obtained. We searched for spectral features of methoxyacetaldehyde in the high-mass star-forming regions Orion KL and Sagittarius B2, as well as in the cold dark cloud Barnard 1 (B1-b). No lines belonging to methoxyacetaldehyde were detected above the detection limit of our data. We provide upper limits to the methoxyacetaldehyde colum density in these sources.