2026ApJ..1000..160Q

CO₂ is an important, stable, and abundant molecule in the Universe, but it is very difficult to detect because it has no observable pure rotational transitions. The unique sensitivity and resolution of the James Webb Space Telescope provide a fresh way to investigate it. CO₂ is typically found in the solid phase (ice) on grain mantles in dense molecular clouds, but is less commonly detected in the gas phase (compared to common molecules such as CO and H₂O) and has mostly been found in protostellar and protoplanetary environments. Here, we report and characterize the first observations of gas-phase CO₂ absorption toward two IR-bright regions of the Galactic Center, thanks to the high sensitivity of JWST. Using an LTE model, we find a CO₂ gas excitation temperature between 20 and 50 K, a column density around 2 × 10¹⁵ cm^–2 and a radial velocity with respect to the local standard of rest consistent with 0. We also report: (1) simultaneous detections of C₂H₂ and HCN absorption bands (near 13.7 and 14.0 μm, respectively), with column density ratios of 1:3 and 3:2 with respect to gas-phase CO₂, and (2) CO₂ ice absorption with an ice-to-gas abundance ratio of 90, consistent with previous findings. We conclude that the absorbing medium is likely in the foreground, most likely from one or more somewhat clumpy cloud(s), located between 0.15 and 4 kpc away from Earth. Additionally, we detected point-like CO₂ emission likely associated with a Galactic Center evolved star (IRS 11SW), which is also spatially coincident with a previously reported X-ray source, raising the possibility that the system is a symbiotic binary.