The Laboratory Millimeter and Submillimeter Rotational Spectrum of Lactaldehyde and an Astronomical Search in Sgr B2(N), Orion-KL, and NGC 6334I

We present a laboratory rotational study of, and astronomical search for, lactaldehyde (CH3CH(OH)CH(O)), one of the simplest chiral molecules that could reasonably be seen in the interstellar medium (ISM), in the millimeter and submillimeter wave regions from 80 to 460 GHz. More than 5000 transitions were assigned to the most stable conformer, and a set of spectroscopic constants was accurately determined. Lactaldehyde is involved in numerous metabolic pathways used by life on Earth, and is a logical step up in complexity from glycolaldehyde (CH(O)CH2OH) which is being detected with increasing regularity in the ISM. We present an accompanying radio astronomical search for lactaldehyde in three high-mass star-forming regions (NGC 6334I, Sgr B2(N), and Orion-KL) as well as in the publicly available data from the ASAI Large Project. Neither molecule is detected in these sources, and we report corresponding upper limits to the column densities. We discuss the potential utility of lactaldehyde in combination with other members of the [C3,H6,O2] isomeric family in probing pathways of chemical evolution in the ISM.