Rotational Spectrum and First Interstellar Detection of 2-Methoxyethanol Using ALMA Observations of NGC 6334I

We use both chirped-pulse Fourier transform and frequency modulated absorption spectroscopy to study the rotational spectrum of 2-methoxyethanol in several frequency regions ranging from 8.7-500 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. 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× 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 × 10^15 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.