2024ApJ...965L..23F

We use both chirped-pulse Fourier transform and frequency-modulated absorption spectroscopy to study the rotational spectrum of 2-methoxyethanol (CH₃OCH₂CH₂OH) in several frequency regions ranging from 8.7 to 500 GHz. The resulting rotational parameters permitted a search for this molecule in Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protocluster NGC 6334I, as well as source B of the low-mass protostellar system IRAS 16293-2422. A total of 25 rotational transitions are observed in the ALMA Band 4 data toward NGC 6334I, resulting in the first interstellar detection of 2-methoxyethanol. A column density of ${1.3}_{-0.9}^{+1.4}\times {10}^{17}$ cm^–2 is derived at an excitation temperature of ${143}_{-39}^{+31}$ K. However, molecular signal is not observed in the Band 7 data toward IRAS 16293-2422B, and an upper-limit column density of 2.5 × 10¹⁵ cm^–2 is determined. Various possible formation pathways-including radical recombination and insertion reactions-are discussed. We also investigate physical differences between the two interstellar sources that could result in the observed abundance variations.