Infrared Band Strength of Molecular Oxygen in Astrophysical Ices

Abstract Some quantity of molecular oxygen (O 2 ) is likely condensed on the surface of interstellar ice mantles, yet this compound has never been detected in the solid phase in the interstellar medium. With the sensitivity of the James Webb Space Telescope, it seems reasonable that future detections could be possible. Here we present measurements of the band strength of the O 2 infrared fundamental (∼6.46 μ m) in a number of representative astrophysical ice environments. We find that in binary ice mixtures of O 2 and H 2 O (or CO 2 ), the band strengths are the same within error (2.2 × 10 −20 + / − 0.3 × 10 −20 cm molecule −1 and 1.9 × 10 −20 + / − 0.3 × 10 −20 cm molecule −1 , respectively), while the band strength in CO mixtures is ∼4x lower. Considering the case where O 2 is mixed with H 2 O at percentages measured in cometary coma, we estimate that it could take as little as 2 hr to reach a signal-to-noise ratio where O 2 could be detected with the MIRI instrument.